Foseco-Ferrous-Foundrymans-Handbook

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Foseco Ferrous Foundryman’s Handbook
Foseco Ferrous
Foundryman’s Handbook
Edited by
John R. Brown
OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI
Butterworth-Heinemann
Linacre House, Jordan Hill, Oxford OX2 8DP
225 Wildwood Avenue, Woburn, MA 01801-2041
A division of Reed Educational and Professional Publishing Ltd
 A member of the Reed Elsevier plc group
First published 2000
© Foseco International Ltd 2000
All rights reserved. No part of this publication
may be reproduced in any material form (including
photocopying or storing in any medium by electronic
means and whether or not transiently or incidentally
to some other use of this publication) without the
written permission of the copyright holder except
in accordance with the provisions of the Copyright,
Designs and Patents Act 1988 or under the terms of a
licence issued by the Copyright Licensing Agency Ltd,
90 Tottenham Court Road, London, England W1P 9HE.
Applications for the copyright holder’s written permission
to reproduce any part of this publication should be
addressed to the publishers
British Library Cataloguing in Publication Data
Brown, John R.
Foseco ferrous foundryman’s handbook.
1. Founding – Handbooks, manuals, etc.
I Title II Foseco International III Foundryman’s handbook
671.2
Library of Congress Cataloguing in Publication Data
Foseco ferrous foundryman’s handbook/revised and edited by John R. Brown.
p. cm.
Includes index.
ISBN 0 7506 4284 X
1 Founding – Handbooks, manuals, etc. 2 Iron founding – Handbooks,
manuals, etc. 3 Cast-iron – Handbooks, manuals, etc. I Title: Ferrous
foundryman’s handbook II Brown John R.
TS235 F35 2000
672.2–dc21 00-033679
ISBN 0 7506 4284 X
Typeset at Replika Press Pvt Ltd, Delhi 110 040, India
Printed and bound in Great Britain
Contents
Preface xi
Acknowledgements xii
Chapter 1 Tables and general data 1
SI units and their relation to other units 1
SI, metric, non-SI and non-metric conversions 2
Conversion table of stress values 5
Areas and volumes of circles, spheres, cylinders etc. 6
The physical properties of metals 7
Densities of casting alloys 9
Approximate bulk densities of common materials 10
Patternmakers’ contraction allowances 11
Volume shrinkage of principal casting alloys 13
Comparison of sieve sizes 14
Calculation of average grain size 15
Calculation of AFS grain fineness number 16
Recommended standard colours for patterns 17
Dust control in foundries 18
Buoyancy forces on cores 18
Opening forces on moulds 19
Dimensional tolerances and consistency achieved in castings 21
Chapter 2 Types of cast iron 23
Introduction 23
Physical properties of cast irons 27
Iron casting processes 28
Chapter 3 Grey cast iron 30
Specifications 30
Relationship between composition, strength and structure of
grey cast iron 32
Applications of grey iron castings 37
The production of grey irons 37
Chapter 4 Melting cast iron 40
Introduction 40
Cupola melting 40
Electric melting 53
Shop floor control of metal composition 60
Chapter 5 Inoculation of grey cast iron 62
Introduction 62
Ladle inoculation 64
Late stream inoculation 66
Mould inoculation 69
Chapter 6 Ductile iron 70
Production of ductile iron 70
Melting ductile iron base 74
Cupola melting and duplexing 74
Induction furnace melting 75
Use of the tundish cover ladle 75
Sandwich treatment 77
NODULANT 77
Pure magnesium converter process 77
Cored wire treatment 78
In-the-mould treatment 78
Inhibiting elements 78
Inoculation and fading 79
Specifications for ductile cast iron 79
Heat treatment of ductile iron 82
Casting ductile iron 84
Compacted graphite irons 84
Chapter 7 Malleable cast iron 90
Introduction 90
Whiteheart malleable 90
Blackheart malleable iron 92
Chapter 8 Special purpose cast irons 95
Heat resisting alloys 95
Corrosion resistant cast irons 101
Wear resistant cast irons 102
vi Contents
Chapter 9 Types of steel castings 108
Introduction 108
Specifications for steel castings 109
Types of steel castings 111
Carbon steels 112
Low alloy and medium alloy steels 112
Austenitic manganese steel 114
High alloy steels 114
Duplex steels 117
Physical properties of steels 117
Selection of suitable steel for casting 117
Chapter 10 Melting and treatment of steel for casting 121
Arc furnace melting 121
Induction furnace melting 123
AOD refining 125
Melting and casting quality 125
Chapter 11 Molten metal handling 130
Iron foundries 130
Metal handling systems 130
Ladle lining 130
KALTEK ladle lining system for iron foundries 132
KALTEK insulating lining system for automatic pouring boxes 136
Casting defects due to poor ladle maintenance 137
Molten metal handling in steel foundries 138
Ladle practice 138
The KALTEK ladle lining system 142
Pouring temperature for steels 144
Chapter 12 Sands and green sand 146
Silica sand 146
Measurement of sand properties 149
Non-silica sands 151
Green sand 152
Parting agents 163
Special moulding materials, LUTRON 163
Green sand moulding machines 164
Contents vii
Chapter 13 Resin bonded sand 167
Chemical binders 167
Self-hardening process 167
Sand reclamation 173
Self-hardening resin binder systems 180
Triggered hardening systems 184
Heat triggered processes 186
Gas triggered processes 192
Review of resin coremaking processes 198
Chapter 14 Sodium silicate bonded sand 204
CO2 silicate process (basic process) 204
Improvements to the CO2 silicate process 207
Self-setting sodium silicate processes 209
Adhesives and sealants 213
Chapter 15 Lost foam casting 216
Principle of the process 216
Patternmaking 217
Assembling clusters 218
Coating the patterns 218
Investing in sand 218
The mechanism of casting into foam patterns 218
Advantages of lost foam casting 221
Disadvantages 222
Applications 222
The future 224
Chapter 16 Coatings for moulds and cores 226
The need for a coating 226
Choice of coating and form of supply 227
Components of a coating 228
Application methods for coatings 230
Coatings for iron and steel foundries 234
Coatings for high production foundries 234
Coatings for jobbing moulds and cores 237
Spirit based coatings 237
The TRIBONOL process 240
Miscellaneous coatings 241
Coatings for foundry tools 243
viii Contents
Chapter 17 Filtration and the running and gating of iron castings 245
Introduction 245
Conventional running systems without filters 245
Filtration of iron castings 250
SEDEX ceramic foam filters 256
Cellular ceramic filters 259
Combined filter, feeder and pouring cup, the KALPUR direct
pouring system 266
Chapter 18 Filtration and the running and gating of steel castings 272
Introduction 272
Controlling the flow of metal 272
Conventional running systems without filters 274
The use of ceramic foam filters 277
Inclusions in steel castings 277
STELEX ZR ceramic foam filters 279
KALPUR ST direct pour unit 286
Cost savings through the use of STELEX and KALPUR 294
Chapter 19 Feeding of castings 296
Introduction 296
Natural feeders 296
Aided feeders – feeding systems 297
The calculation of feeder dimensions 301
Determination of feeding requirements 305
Steel, malleable iron, white irons, light alloys and copper based
alloy castings 305
Grey and ductile irons 307
Foseco feeding systems 310
KALPUR filter feeder units 322
Breaker cores 323
Application of feeder sleeves 325
FERRUX anti-piping compounds for iron and steel castings 331
Aids to the calculation of feeder requirements 334
FEEDERCALC 335
Chapter 20 Computer simulation of casting processes 344
Introduction 344
Solidification modelling 344
Contents ix
Mould filling simulation 346
The SOLSTAR solidification program 346
Cost benefits of solidification simulation 351
Conclusions 352
Index 353
x Contents
Preface
The last edition of the Foseco Foundryman’s Handbook was published in 1994
and like all the earlier editions, it aimed to provide a practical reference
book for all those involved in making castings in any of the commonly used
alloys by any of the usual moulding methods. In order to keep the Handbook
to a reasonable size, it was not possible to deal with all thecommon casting
alloys in detail. Since 1994 the technology of casting has continued to develop
and has become more specialised so that it has been decided to publish the
new edition of the Handbook in two volumes:
Ferrous dealing with grey, ductile and special purpose cast irons
together with carbon, low alloy and high alloy steels
Non-ferrous dealing with aluminium, copper and magnesium casting
alloys
Certain chapters (with slight modifications) are common to both volumes:
these chapters include tables and general data, sands and sand bonding
systems, resin bonded sand, sodium silicate bonded sand and feeding systems.
The remaining chapters have been written specifically for each volume.
The Handbook refers to many Foseco products. Not all of the products are
available in every country and in a few cases, product names may vary.
Users should always contact their local Foseco company to check whether
a particular product or its equivalent is available.
The Foseco logo and all product names appearing in capital letters are
trademarks of the Foseco group of companies, used under licence.
John R. Brown
Acknowledgements
The following Organisations have generously permitted the use of their
material in this book:
The American Foundryman’s Society Inc., 505 State Street, Des Plaines,
Illinois 60016-8399, USA
British Standards Institution (BSI), Extracts from British Standards are
reproduced with the permission of BSI. Complete copies can be obtained
by post from BSI Customer Services, 389 Chiswick High Road, London
W4 4AL
Butterworth-Heinemann, Linacre House, Jordan Hill, Oxford OX2 8DP
The Castings Development Centre (incorporating BCIRA), Bordesley Hall,
The Holloway, Alvechurch, Birmingham, B48 7QB
The Castings Development Centre (incorporating Steel Castings Research
& Trade Association), 7 East Bank Road, Sheffield, S2 3PT
The Department of the Environment, Transport and the Regions
Foundry Management & Technology, Penton Media Inc., 1100 Superior
Avenue, Cleveland OH 44114-2543, USA
Foundry & Technical Liaison Ltd., 6–11 Riley Street, Willenhall, West Midlands,
WV13 1RV
Institute of British Foundrymen, Bordesley Hall, The Holloway, Alvechurch,
Birmingham, B48 7QA
Rio Tinto Iron & Titanium GmbH, Eschborn, Germany
SinterCast Ltd, Regal House, 70 London Road, Twickenham, Middlesex
The author gratefully acknowledges the help received from colleagues at
Foseco International Limited, Foseco UK Limited and other Foseco Companies.
Chapter 1
Tables and general data
SI units and their relation to other units
The International System of Units (SI System) is based on six primary
units:
Quantity Unit Symbol
length metre m
mass kilogram kg
time second s
electric current ampere A
temperature degree Kelvin K
luminous intensity candela cd
Multiples
SI prefixes are used to indicate multiples and submultiples such as 106
or 10–3
Prefix Symbol Prefix Symbol
10 deca da 10–1 deci d
102 hecto h 10–2 centi c
103 kilo k 10–3 milli m
106 mega M 10–6 micro µ
109 giga G 10–9 nano n
1012 tera T 10–12 pico p
Example: One millionth of a metre is expressed as one micrometre, 1 µm.
2 Foseco Ferrous Foundryman’s Handbook
Derived units
The most important derived units for the foundryman are:
Quantity Unit Symbol
Force newton N (kg m/s2)
Pressure, stress newton per square metre or pascal N/m2 (Pa)
Work, energy joule J (Nm)
Power, heat flow rate watt, joule per second W (J/s)
Temperature degree Celsius °C
Heat flow rate watt per square metre W/m2
Thermal conductivity watt per metre degree W/m K
Specific heat capacity joule per kilogram degree J/kg K
Specific latent heat joule per kilogram J/kg
SI, metric, non-SI and non-metric conversions
Length:
1 in = 25.4 mm
1 ft = 0.3048 m
1 m = 1.09361 yd
1 km = 1093.61 yd = 0.621371 miles
1 mile = 1.60934 km = 1760 yd
1 yd = 0.9144 m
Area:
1 in2 = 654.16 mm2
1 ft2 = 0.092903 m2
1 m2 = 1.19599 yd2 = 10.76391 ft2
1 mm2 = 0.00155 in2
1 yd2 = 0.836127 m2
1 acre = 4840 yd2 = 4046.86 m2 = 0.404686 m2 hectare
1 hectare = 2.47105 acre = 10 000 m2
Volume:
1 cm3 = 0.061024 in3
1 dm3 = 11 (litre) = 0.035315 ft3
1 ft3 = 0.028317 m3 = 6.22883 gal (imp)
1 gal (imp) = 4.54609 l (litre)
1 in3 = 16.3871 cm3
1 l (litre) = 1 dm3 = 0.001 m3 = 0.21997 gal (imp)
1 m3 = 1.30795 yd3 = 35.31467 ft3
1 pt (pint) = 0.568261 l
1 US gal = 3.78541 l = 0.832674 gal (imp)
Tables and general data 3
1 ft3/min (cfm) = 1.699 m3/h
1 ft3/sec = 28.31681/s
Mass:
1 lb (pound) = 0.453592 kg
1 cwt = 50.802 kg
1 kg = 2.20462 lb
1 oz = 28.349 gm
1 ton = 2240 lb = 1.01605 t (tonne) = 1016.05 kg
1 ton (US) = 2000 lb = 907.185 kg
Force:
1 kgf = 9.80665 N = 2.20462 lbf = 1 kp (kilopond)
1 lbf = 4.44822 N
1 pdl (poundal) = 0.138255 N
Density:
1 kgf/m3 = 0.062428 lb/ft3
1 lb/ft3 = 16.0185 kg/m3
1 g/cm3 = 1000 kg/m3
Pressure, stress:
1 kgf/cm2 = 98.0665 kPa (kN/m2)
1 kgf/mm2 = 9.80665 N/mm2 = 1422.33 lbf/in2 = 0.63497 tonf/in2
1 lbf/in2 (psi) = 6.89476 kPa (kN/m2)
1 Pa (N/m2) = 0.000145038 lbf/in2
1 in w.g. (in H2O) = 249.089 Pa
1 N/mm2 = 1 MPa = 145.038 lbf/in2 = 0.06475 tonf/in2
= 0.10197 kgf/cm2
Power:
1 kW = 3412 Btu/hr
1 hp (horsepower) = 0.745700 kW
Energy, heat, work:
1 Btu = 1.05506 kJ
1 cal = 4.1868 J
1 kWh = 3.6 MJ = 3412 Btu
1 therm = 100 000 Btu = 105.506 MJ
1 kJ = 0.277778 W.h
Specific heat capacity, heat transfer:
1 cal/g°C = 1 kcal/kg°C = 4186.8 J/kg.K
1 Btu/lb°F = 4186.8 J/kg.K
1 Btu/h = 0.293071 W
1 cal/cm.s°C = 418.68 W/m.K (thermal conductivity)
4 Foseco Ferrous Foundryman’s Handbook
1 Btu.in/ft2h°F = 0.144228 W/m.K (thermal conductivity)
1 Btu/ft2h°F = 5.67826 W/m2.K (heat transfer coeff.)
Miscellaneous:
1 std.atmos. = 101.325 kPa = 760 mm Hg = 1.01325 bar
1 bar = 100 kPa = 14.5038 lbf/in2
1 cP (centipoise) = 1 mPa.s
1 cSt (centistoke) = 1 mm2/s
1 cycle/s = 1 Hz (Hertz)
1 hp = 745.7 W
Useful approximations:
1 Btu = 1 kJ 1 kg = 21/4 lb
1 ft = 30 cm 1 kgf = 10 N
1 gal = 41/2 l 1 std atmos. = 1 bar
1 ha = 21/2 acre 1 km = 5/8 mile
1 hp = 3/4 kW 1 litre = 13/4 pint
1 in = 25 mm 1 lbf = 41/2 N
1 therm = 100 MJ 1 yd = 0.9 m
1 tonf/in2 = 15 N/mm2
1 psi (lbf/in2) = 7 kPa
1 N (newton) = the weight of a small apple!
Temperature:
°F = 1.8 × °C + 32
°C = (°F – 32)/1.8
0°C (Celsius) = 273.15 K (Kelvin)
Tables and general data 5
Conversion table of stress values
Equivalent stresses
American British Metric SI
(lb/in2) (ton/in2) (kgf/mm2) (N/mm2)
250 0.112 0.176 1.724
500 0.223 0.352 3.447
1000 0.446 0.703 6.895
2000 0.893 1.406 13.789
3000 1.339 2.109 20.684
4000 1.788 2.812 27.579
5000 2.232 3.515 34.474
10 000 4.464 7.031 68.947
15 000 6.696 10.546 103.421
20 000 8.929 14.062 137.894
25 000 11.161 17.577 172.368
30 000 13.393 21.092 206.841
35 000 15.652 24.608 241.315
40 000 17.875 28.123 275.788
45 000 20.089 31.639 310.262
50 000 22.321 35.154 344.735
55 000 24.554 38.670 379.209
60 000 26.786 42.185 413.682
65 000 29.018 45.700 448.156
70 000 31.250 49.216 482.629
75 000 33.482 52.731 517.103
80 000 35.714 56.247 551.576
85 000 37.946 59.762 586.050
90 000 40.179 63.277 620.523
95 000 42.411 66.793 654.997
100 000 44.643 70.308 689.470
Conversions
10 000 4.464 7.031 68.947
22 399 10 15.749 154.438
14 223 6.349 10 98.066
14 504 6.475 10.197 100
6 Foseco Ferrous Foundryman’s Handbook
Areas and volumes of circles, spheres, cylinders etc.
π = 3.14159 (approximation: 22/7)
1 radian = 57.296 degrees
Circle; radius r, diameter d:
circumference = 2πr = πd
area = πr2 = π/4 × d2
Sphere; radius r:
surface area = 4 πr2
volume = 4/3 πr3
Cylinder; radius of base r, height h:
area of curved surface = 2πrh
volume = πr2h
Cone; radius of base r, height h:
volume = 1/2 area of base × height
= 1/2 πr2h
Triangle; base b, height h:
area = 1/2bh
Tables and general data 7
The physical properties of metals
Element Symbol Atomic Melting Boiling Latent heat of Mean specific heat
weight point point fusion 0–100°C
(°C) (°C)
(kJ/kg) (cal/g) (kJ/kg.K) (cal/g°C)
Aluminium Al 26.97 660.4 2520 386.8 92.4 0.917 0.219
Antimony Sb 121.76630.7 1590 101.7 24.3 0.209 0.050
Arsenic As 74.93 volat. 616 – – 0.331 0.079
Barium Ba 137.37 729 2130 – – 0.285 0.068
Beryllium Be 9.02 1287 2470 133.5 31.9 2.052 0.490
Bismuth Bi 209.0 217.4 1564 54.4 13.0 0.125 0.030
Cadmium Cd 112.41 321.1 767 58.6 14.0 0.233 0.056
Calcium Ca 40.08 839 1484 328.6 78.5 0.624 0.149
Carbon C 12.01 – – – – 0.703 0.168
Cerium Ce 140.13 798 3430 – – 0.188 0.045
Chromium Cr 52.01 1860 2680 132.7 31.7 0.461 0.110
Cobalt Co 58.94 1494 2930 244.5 58.4 0.427 0.102
Copper Cu 63.57 1085 2560 180.0 43.0 0.386 0.092
Gallium Ga 69.74 29.7 2205 80.2 19.2 0.377 0.090
Gold Au 197.2 1064.4 2860 67.4 16.1 0.130 0.031
Indium In 114.8 156 2070 – – 0.243 0.058
Iridium Ir 193.1 2447 4390 – – 0.131 0.031
Iron Fe 55.84 1536 2860 200.5 47.9 0.456 0.109
Lead Pb 207.22 327.5 1750 20.9 5.0 0.130 0.031
Lithium Li 6.94 181 1342 137.4 32.8 3.517 0.840
Magnesium Mg 24.32 649 1090 194.7 46.5 1.038 0.248
Manganese Mn 54.93 1244 2060 152.8 36.5 0.486 0.116
Mercury Hg 200.61 –38.9 357 12.6 3.0 0.138 0.033
Molybdenum Mo 96.0 2615 4610 – – 0.251 0.060
Nickel Ni 58.69 1455 2915 305.6 73.0 0.452 0.108
Niobium Nb 92.91 2467 4740 – – 0.268 0.064
Osmium Os 190.9 3030 5000 – – 0.130 0.031
Palladium Pd 106.7 1554 2960 150.7 36.0 0.247 0.059
Phosphorus P 31.04 44.1 279 20.9 5.0 0.791 0.189
Platinum Pt 195.23 1770 3830 113.0 27.0 0.134 0.032
Potassium K 39.1 63.2 759 67.0 16.0 0.754 0.180
Rhodium Rh 102.91 1966 3700 – – 0.243 0.058
Silicon Si 28.3 1412 3270 502.4 120.0 0.729 0.174
Silver Ag 107.88 961.9 2163 92.1 22.0 0.234 0.055
Sodium Na 23.00 97.8 883 115.1 27.5 1.227 0.293
Strontium Sr 87.63 770 1375 – – 0.737 0.176
Sulphur S 32.0 115 444.5 32.7 9.0 0.068 0.016
Tantalum Ta 180.8 2980 5370 154.9 37.0 0.142 0.034
Tellurium Te 127.6 450 988 31.0 7.4 0.134 0.032
Thallium Tl 204 304 1473 – – 0.130 0.031
Tin Sn 118.7 232 2625 61.1 14.6 0.226 0.054
Titanium Ti 47.9 1667 3285 376.8 90.0 0.528 0.126
Tungsten W 184.0 3387 5555 167.5 40.0 0.138 0.033
Uranium U 238.2 1132 4400 – – 0.117 0.029
Vanadium V 50.95 1902 3410 334.9 80.0 0.498 0.119
Zinc Zn 65.38 419.6 911 110.1 26.3 0.394 0.094
Zirconium Zr 90.6 1852 4400 – – 0.289 0.069
8 Foseco Ferrous Foundryman’s Handbook
The physical properties of metals (continued)
Element Thermal Resistivity Vol. change Density Coeff. of Brinell
conductivity (µohm.cm on melting (g/cm3) expansion hardness
(W/m.K) at 20°C) (%) (× 10–6/K) no.
Al 238 2.67 6.6 2.70 23.5 17
Sb 23.8 40.1 1.4 6.68 11 30
As – 33.3 – 5.73 5.6 –
Ba – 60 – 3.5 18 –
Be 194 3.3 – 1.85 12 –
Bi 9 117 –3.3 9.80 13.4 9
Cd 103 7.3 4.7 8.64 31 20
Ca 125 3.7 – 1.54 22 13
C 16.3 – – 2.30 7.9 –
Ce 11.9 85.4 – 6.75 8 –
Cr 91.3 13.2 – 7.10 6.5 350
Co 96 6.3 – 8.90 12.5 125
Cu 397 1.69 4.1 8.96 17 48
Ga 41 – – 5.91 18.3 –
Au 316 2.2 5.2 19.3 14.1 18.5
In 80 8.8 – 7.3 24.8 1
Ir 147 5.1 – 22.4 6.8 172
Fe 78 10.1 5.5 7.87 12.1 66
Pb 35 20.6 3.4 11.68 29 5.5
Li 76 9.3 1.5 0.53 56 –
Mg 156 4.2 4.2 1.74 26 25
Mn 7.8 160 – 7.4 23 –
Hg 8.7 96 3.75 13.55 61 –
Mo 137 5.7 – 10.2 5.1 147
Ni 89 6.9 – 8.9 13.3 80
Nb 54 16 – 8.6 7.2 –
Os 87 8.8 – 22.5 4.6 –
Pd 75 10.8 – 12.0 11.0 50
P – – – 1.83 6.2 –
Pt 73 10.6 – 21.45 9.0 52
K 104 6.8 2.8 0.86 83 0.04
Rh 148 4.7 – 12.4 8.5 156
Si 139 103–106 – 2.34 7.6 –
Ag 425 1.6 4.5 10.5 19.1 25
Na 128 4.7 2.5 0.97 71 0.1
Sr – 23 – 2.6 100 –
S 272 – – 2.07 70 –
Ta 58 13.5 – 16.6 6.5 40
Te 3.8 1.6 × 105 – 6.24 – –
Tl 45.5 16.6 – 11.85 30 –
Sn 73.2 12.6 2.8 7.3 23.5 –
Ti 21.6 54 – 4.5 8.9 –
W 174 5.4 – 19.3 4.5 –
U 28 27 – 19.0 – –
V 31.6 19.6 – 6.1 8.3 –
Zn 120 6.0 6.5 7.14 31 35
Zr 22.6 44 – 6.49 5.9 –
Tables and general data 9
Densities of casting alloys
Alloy BS1490 g/ml Alloy BS1400 g/ml
Aluminium alloys Copper alloys
Pure Al 2.70 HC copper HCC1 8.9
Al–Si5Cu3 LM4 2.75 Brass CuZn38Al DCB1 8.5
Al–Si7Mg LM25 2.68 CuZn33Pb2Si HTB1 8.5
Al–Si8Cu3Fe LM24 2.79 CuZn33Pb2 SCB3 8.5
AlSi12 LM6 2.65 Phosphor bronze
CuSn11P PB1 8.8
Cast steels CuSn12 PB2 8.7
Low carbon <0.20 7.86 Lead bronze
Med. carbon 0.40 7.86 CuSn5Pb20 LB5 9.3
High carbon >0.40 7.84 Al bronze
CuAl10Fe2 AB1 7.5
Low alloy 7.86 Gunmetal
Med. alloy 7.78 CuSnPb5Zn5 LG2 8.8
Med./high alloy 7.67 Copper nickel
CuNi30Cr2FeMnSi CN1 8.8
Stainless
13Cr 7.61 Cast irons
18Cr8Ni 7.75 Grey iron 150 MPa 6.8–7.1
200 7.0–7.2
Other alloys 250 7.2–7.4
Zinc base 300 7.3–7.4
ZnAl4Cu1 6.70 Whiteheart malleable 7.45
Blackheart malleable 7.27
Lead base White iron 7.70
PbSb6 10.88 Ductile iron (s.g.) 7.2–7.3
Tin base (Babbit) 7.34 Ni-hard 7.6–7.7
Inconel Ni76Cr18 8.50 High silicon (15%) 6.8
10 Foseco Ferrous Foundryman’s Handbook
Approximate bulk densities of common materials
Material kg/m3 lb/ft3 Material kg/m3 lb/ft3
Aluminium, cast 2560 160 Lead 11370 710
wrought 2675 167 Limestone 2530–2700 158–168
Aluminium bronze 7610 475
Ashes 590 37 Magnesite 2530 158
Mercury 13 560 847
Brass, rolled 8390 524 Monel 8870 554
swarf 2500 175
Babbit metal 7270 454 Nickel, cast 8270 516
Brick, common 1360–1890 85–118 Nickel silver 8270 516
fireclay 1840 115
Bronze 8550 534 Phosphor bronze 8580 536
Pig iron, mean 4800 300
Cast iron, solid 7210 450 Pig iron and scrap
turnings 2240 140 (cupola charge) 5400 336
Cement, loose 1360 85
Chalk 2240 140 Sand, moulding 1200–1440 75–90
Charcoal, lump 290 18 silica 1360–1440 85–90
Clay 1900–2200 120–135 Silver, cast 10 500 656
Coal 960–1280 60–80 Steel 7850 490
Coal dust 850 53
Coke 450 28 Tin 7260 453
Concrete 2240 140
Copper, cast 8780 548 Water, ice 940 58.7
Cupola slag 2400 150 liquid 0°C 1000 62.4
100°C 955 59.6
Dolomite 2680 167 Wood, balsa 100–130 7–8
oak 830 52
Fire clay 1440 90 pine 480 30
French chalk 2600 162 teak 640 40
Wrought iron 7700 480
Glass 2230 139
Gold, pure 19 200 1200 Zinc, cast 6860 428
22 carat 17 500 1090 rolled 7180 448
Graphite, powder 480 30
solid 2200 138
Tables and general data 11
Patternmakers’ contraction allowances
Castings are always smaller in dimensions than the pattern from which
they are made, because as the metal cools from its solidification temperature
to room temperature, thermal contraction occurs. Patternmakers allow for
this contraction by making patterns larger in dimensions than the required
castings by an amount known as the “contraction allowance”. Originally
this was done by making use of specially engraved rules, known as
“contraction rules”, the dimensions of which incorporated a contraction
allowance such as 1 in 75 for aluminium alloys, or 1 in 96 for iron castings.
Nowadays, most patterns and coreboxes are made using computer-controlled
machine tools and it is more convenient to express the contraction as a
percentage allowance.
Predicting casting contraction can never be precise, since many factors
are involved in determining the exact amount of contraction that occurs.
For example, when iron castings are made in greensand moulds, the mould
walls may move under the pressure of the liquid metal, causing expansion
of the mould cavity, thus compensating for some of the metal contraction.
Cored castings may not contract as much as expected, because the presence
of a strong core may restrict movement of the casting as it is cooling. Some
core binders expand with the heat of the cast metal causing the casting to be
larger than otherwise expected. For these reasons, and others, it is only
possible to predict contractions approximately, but if a patternmaker works
with a particular foundry for a long period, he will gain experience with the
foundry’s design of castings and with the casting methods used in the
foundry. Based on such experience, more precise contraction allowances
can be built into the patterns.
12 Foseco Ferrous Foundryman’s Handbook
The usually accepted contraction allowances for different alloys are given
in the following table.
Alloy Contraction allowance (%)
Aluminium alloys
Al–Si5Cu3 LM4
Al–Si7Mg LM25 1.3
Al–Si8Cu3Fe LM24
Al–Si12 LM6
Beryllium copper 1.6
Bismuth 1.3
Brass 1.56
Bronze, aluminium 2.32
manganese 0.83–1.56
phosphor 1.0–1.6
silicon 1.3–1.6
Cast iron, grey 0.9–1.04
white 2.0
ductile (s.g.) 0.6–0.8
malleable 1.0–1.4Copper 1.6
Gunmetal 1.0–1.6
Lead 2.6
Magnesium alloys 1.30–1.43
Monel 2.0
Nickel alloys 2.0
Steel, carbon 1.6–2.0
chromium 2.0
manganese 1.6–2.6
Tin 2.0
White metal 0.6
Zinc alloys 1.18
Tables and general data 13
Volume shrinkage of principal casting alloys
Most alloys shrink in volume when they solidify, the shrinkage can cause
voids in castings unless steps are taken to “feed” the shrinkage by the use
of feeders.
Casting alloy Volume shrinkage (%)
Carbon steel 6.0
Alloyed steel 9.0
High alloys steel 10.0
Malleable iron 5.0
Al 8.0
Al–Cu4Ni2Mg 5.3
Al–Si12 3.5
Al–Si5Cu2Mg 4.2
Al–Si9Mg 3.4
Al–Si5Cu1 4.9
Al–Si5Cu2 5.2
Al–Cu4 8.8
Al–Si10 5.0
Al–Si7NiMg 4.5
Al–Mg5Si 6.7
Al–Si7Cu2Mg 6.5
Al–Cu5 6.0
Al–Mg1Si 4.7
Al–Zn5Mg 4.7
Cu (pure) 4.0
Brass 6.5
Bronze 7.5
Al bronze 4.0
Sn bronze 4.5
14 Foseco Ferrous Foundryman’s Handbook
Comparison of sieve sizes
Sieves used for sand grading are of 200 mm diameter and are now usually
metric sizes, designated by their aperture size in micrometres (µm). The
table lists sieve sizes in the British Standard Metric series (BS410 : 1976)
together with other sieve types.
Sieve aperture, micrometres and sieve numbers
ISO/R.565 series BSS ASTM
(BS410:1976)
(µm) No. µm No. µm
(1000) 16 1003 18 1000
710 22 699 22 710
500 30 500 30 500
355 44 353 45 350
250 60 251 60 250
(212) 72 211 70 210
180
(150) 100 152 100 149
125 120 125
90 150 104 150 105
63 200 76 200 74
(45) 300 53 325 44
Notes: The 1000 and 45 sieves are optional.
The 212 and 150 sieves are also optional, but may be included to give better
separation between the 250 and 125 sieves.
Tables and general data 15
Calculation of average grain size
The adoption of the ISO metric sieves means that the old AFS grain fineness
number can no longer be calculated. Instead, the average grain size, expressed
as micrometres (µm) is now used. This is determined as follows:
1 Weigh a 100 g sample of dry sand.
2 Place the sample into the top sieve of a nest of ISO sieves on a vibrator.
Vibrate for 15 minutes.
3 Remove the sieves and, beginning with the top sieve, weigh the quantity
of sand remaining on each sieve.
4 Calculate the percentage of the sample weight retained on each sieve,
and arrange in a column as shown in the example.
5 Multiply the percentage retained by the appropriate multiplier and add
the products.
6 Divide by the total of the percentages retained to give the average grain
size.
Example
ISO aperture Percentage Multiplier Product
(µm) retained
≥ 710 trace 1180 0
500 0.3 600 180
355 1.9 425 808
250 17.2 300 5160
212 25.3 212 5364
180 16.7 212 3540
150 19.2 150 2880
125 10.6 150 1590
90 6.5 106 689
63 1.4 75 105
≤63 0.5 38 19
Total 99.6 – 20 335
Average grain size = 20 335/99.6
= 204 µm
16 Foseco Ferrous Foundryman’s Handbook
Calculation of AFS grain fineness number
Using either the old BS sieves or AFS sieves, follow, steps 1–4 above.
5 Arrange the results as shown in the example below.
6 Multiply each percentage weight by the preceding sieve mesh number.
7 Divide by the total of the percentages to give the AFS grain fineness
number.
Example
BS sieve % sand retained Multiplied by Product
number on sieve previous sieve no.
10 nil – –
16 nil – –
22 0.2 16 3.2
30 0.8 22 17.6
44 6.7 30 201.0
60 22.6 44 1104.4
100 48.3 60 2898.0
150 15.6 100 1560.0
200 1.8 150 270.0
pan 4.0 200 800.0
Total 100.0 – 6854.2
AFS grain fineness number = 6854.2/100
= 68.5 or 68 AFS
Foundry sands usually fall into the range 150–400 µm, with 220–250 µm
being the most commonly used. Direct conversion between average grain
size and AFS grain fineness number is not possible, but an approximate
relation is shown below:
AFS grain
fineness no. 35 40 45 50 55 60 65 70 80 90
Average
grain size (µm) 390 340 300 280 240 220 210 195 170 150
While average grain size and AFS grain fineness number are useful
parameters, choice of sand should be based on particle size distribution.
Tables and general data 17
Recommended standard colours for patterns
Part of pattern Colour
As-cast surfaces which are to be left unmachined Red or orange
Surfaces which are to be machined Yellow
Core prints for unmachined openings and end prints
Periphery Black
Ends Black
Core prints for machined openings Periphery Yellow stripes
on black
Ends Black
Pattern joint (split patterns) Cored section Black
Metal section Clear varnish
Touch core Cored shape Black
Legend “Touch”
Seats of and for loose pieces Green
and loose core prints
Stop offs Diagonal black
stripes with
clear varnish
Chilled surfaces Outlined in Black
Legend “Chill”
18 Foseco Ferrous Foundryman’s Handbook
Dust control in foundries
Air extraction is used in foundries to remove silica dust from areas occupied
by operators. The following table indicates the approximate air velocities
needed to entrain sand particles.
Terminal velocities of spherical particles of density 2.5 g/cm3 (approx.)
BS sieve Particle Terminal velocity
size dia. (µm) m/sec ft/sec ft/min
16 1003 7.0 23 1400
30 500 4.0 13 780
44 353 2.7 9 540
60 251 1.8 6 360
100 152 1.1 3.5 210
150 104 0.5 1.7 100
200 76 0.4 1.3 80
For the comfort and safety of operators, air flows of around 0.5 m/sec are
needed to carry away silica dust. If air flow rate is too high, around the
shake-out for example, there is a danger that the grading of the returned
sand will be altered.
Buoyancy forces on cores
When liquid metal fills a mould containing sand cores, the cores tend to
float and must be held in position by the core prints or by chaplets. The
following table lists the buoyancy forces experienced by silica sand
cores in various liquid metals, expressed as a proportion of the weight of
the core:
Liquid metal Ratio of buoyant force to core weight
Aluminium 0.66
Brass 4.25
Copper 4.50
Cast iron 3.50
Steel 3.90
Core print support
Moulding sand (green sand) in a core print will support about 150 kN/m2
(21 psi). So the core print can support the following load:
Tables and general data 19
Support (kN) = Core print area (m2) × 150
1 kN = 100 kgf (approx.)
Support (kgf) = Core print area (m2) × 15 000
Example: A core weighing 50 kg has a core print area of 10 × 10 cm (the area
of the upper, support surface), i.e. 0.1 × 0.1 = 0.01 m2. The print support is
150 × 0.01 = 1.5 kN = 150 kgf.
If the mould is cast in iron, the buoyancy force is 50 × 3.5 = 175 kgf so
chaplets may be necessary to support the core unless the print area can be
increased.
Opening forces on moulds
Unless a mould is adequately clamped or weighted, the force exerted by the
molten metal will open the boxes and cause run-outs. If there are insufficient
box bars in a cope box, this same force can cause other problems like distortion
and sand lift. It is important therefore to be able to calculate the opening
force so that correct weighting or clamping systems can be used.
The major force lifting the cope of the mould is due to the metallostatic
pressure of the molten metal. This pressure is due to the height, or head, of
metal in the sprue above the top of the mould (H in Fig. 1.1). Additional
forces exist from the momentum of the metal as it fills the mould and from
forces transmitted to the cope via the core prints as the cores in cored castings
try to float.
Figure 1.1 Opening forces of moulds.
Ladle
h
H
Bush
F
Cope
Area A
Drag
The momentum force is difficult to calculate but can be taken into account
by adding a 50% safety factor to the metallostatic force.
20 Foseco Ferrous Foundryman’s Handbook
The opening metallostatic force is calculated from the total upward-facing
area of the cope mould in contact with the metal (this includes the area of
all the mould cavities in the box). The force is:
 
F A H d(kgf) = 1.5
1000
× × ×
A is the upward facing area in cm2
H (cm) is the height of the top of the sprue above the average height of the
upward facing surface
d is the density of the molten metal (g/cm3)
1.5 is the “safety factor”
For ferrous metals, d is about 7.5, so:
 
F A H(kgf)= 11 
1000
× ×
For aluminium alloys, d is about 2.7, so:
 
F A H(kgf) = 4 
1000
× ×
Forces on cores
The core tends to float in the liquid metal and exerts a further upward force
(see page 18)
In the case of ferrous castings, this force is
3.5 × W (kgf)
where W is the weight of the cores in the mould (in kg).
In aluminium, the floating force can be neglected.
The total resultant force on the cope is (for ferrous metals)
(11 × A × H)/1000 + 3.5 W kgf
Example: Consider a furane resin mould for a large steel valve body casting
having an upward facing area of 2500 cm2 and a sprue height (H) of 30 cm
with a core weighing 40 kg. The opening force is
11 × 2500 × 30/1000 + 3.5 × 40 = 825 + 140
= 965 kgf
It is easy to see why such large weights are needed to support moulds in
jobbing foundries.
Tables and general data 21
Dimensional tolerances and consistency
achieved in castings
Errors in dimensions of castings are of two kinds:
Accuracy: the variation of the mean dimension of the casting from
the design dimension given on the drawing
Consistency: statistical errors, comprising the dimensional variability
round the mean dimension
Dimensional accuracy
The major causes of deviations of the mean dimension from the target value
are contraction uncertainty and errors in pattern dimensions. It is usually
possible to improve accuracy considerably by alternations to pattern
equipment after the first sample castings have been made.
Figure 1.2 The average tolerance (taken as 2.5σ) exhibited by various casting
processes. (From Campbell, J. (1991) Castings, Butterworth-Heinemann, reproduced
by permission of the publishers.)
To
le
ra
nc
e 
(2
.5
σ )
 (
m
m
)
100
10
1
0.1
0.01
S
an
d 
ca
st
in
g
Steel
AI + malleable
White cast iron
Grey cast
iron
AI
Pressure die
Zn
Pressure die
Investment
AI and steel
AI
Precision sand
core assembly
AI
Gravity die and
low-pressure die
10 100 1000 10 000
Casting dimension (mm)
22 Foseco Ferrous Foundryman’s Handbook
Dimensional consistency
Changes in process variables during casting give rise to a statistical spread
of measurements about a mean value. If the mean can be made to coincide
with the nominal dimension by pattern modification, the characteristics of
this statistical distribution determine the tolerances feasible during a
production run.
The consistency of casting dimensions is dependent on the casting process
used and the degree of process control achieved in the foundry. Figure 1.2
illustrates the average tolerance exhibited by various casting processes. The
tolerance is expressed as 2.5σ (2.5 standard deviations), meaning that only
1 casting in 80 can be expected to have dimensions outside the tolerance.
There is an International Standard, ISO 8062–1984(E) Castings – System of
dimensional tolerances, which is applicable to the dimensions of cast metals
and their alloys produced by sand moulding, gravity diecasting, low pressure
diecasting, high pressure diecasting and investment casting. The Standard
defines 16 tolerance grades, designated CT1 to CT16, listing the total casting
tolerance for each grade on raw casting dimensions from 10 to 10 000 mm.
The Standard also indicates the tolerance grades which can be expected for
both long and short series production castings made by various processes
from investment casting to hand-moulded sand cast.
Reference should be made to ISO 8062 or the equivalent British Standard
BS6615:1985 for details.
Chapter 2
Types of cast iron
Introduction
The first iron castings to be made were cast directly from the blast furnace.
Liquid iron from a blast furnace contains around 4%C and up to 2%Si,
together with other chemical elements derived from the ore and other
constituents of the furnace charge. The presence of so much dissolved carbon
etc. lowers the melt point of the iron from 1536°C (pure iron) to a eutectic
temperature of about 1150°C (Fig. 2.1) so that blast furnace iron is fully
liquid and highly fluid at temperatures around 1200°C. When the iron
solidifies, most of the carbon is thrown out of solution in the form either of
graphite or of iron carbide, Fe3C, depending on the composition of the iron,
the rate of cooling from liquid to solid and the presence of nucleants.
If the carbon is precipitated as flake graphite, the casting is called ‘grey
iron’, because the fractured surface has a dull grey appearance due to the
presence of about 12% by volume of graphite. If the carbon precipitates as
carbide, the casting is said to be ‘white iron’ because the fracture has a shiny
white appearance. In the early days of cast iron technology, white iron was
of little value, being extremely brittle and so hard that it was unmachinable.
Grey iron, on the other hand, was soft and readily machined and although
it had little ductility, it was less brittle than white iron.
Iron castings were made as long ago as 500 BC (in China) and from the
15th century in Europe, when the blast furnace was developed. The great
merits of grey iron as a casting alloy, which still remain true today, are its
low cost, its high fluidity at modest temperatures and the fact that it freezes
with little volume change, since the volume expansion of the carbon
precipitating as graphite compensates for the shrinkage of the liquid iron.
This means that complex shapes can be cast without shrinkage defects.
These factors, together with its free-machining properties, account for the
continuing popularity of grey cast iron, which dominates world tonnages of
casting production (Table 2.1).
Greater understanding of the effect of chemical composition and of
nucleation of suitable forms of graphite through inoculation of liquid iron,
has vastly improved the reliability of grey iron as an engineering material.
Even so, the inherent lack of ductility due to the presence of so much graphite
precipitated in flake form (Fig. 2.2) limits the applications to which grey
iron can be put.
A malleable, or ductile form of cast iron was first made by casting ‘white
24 Foseco Ferrous Foundryman’s Handbook
iron’ and then by a long heat treatment process, converting the iron carbide
to graphite. Under the right conditions the graphite developed in discrete,
roughly spherical aggregates (Fig. 2.3) so that the casting became ductile
with elongation of 10% or more. The first malleable iron, ‘whiteheart iron’
Figure 2.1 The iron–carbon phase diagram. (From Elliott, R., Cast Iron Technology,
1988, Butterworth-Heinemann, reproduced by permission of the publishers.)
Te
m
pe
ra
tu
re
 (
°C
)
1600
1200
800
400
0 2 4 6
wt. %C
α + Fe3C
or
α + G
α D
γ + Fe3C
or
γ + G
γ
α + γ
B
δ + γ
δ
δ + liquid
liquidγ +
liquid
A
G + liquid
Fe3C + liquid
C
Fe – G system Fe – Fe3C system
A B C D
(––) Fe–G 2.09 4.25 0.68 %C
1154 1154 739 °C
(---) Fe–Fe3C 2.12 4.31 6.68 0.76 %C
1148 1148 1226 727 °C
Table 2.1 Breakdown of iron casting tonnages 1996 (1000s tonnes)
Total iron Grey iron Ductile iron Malleable iron
Germany
France 6127 3669 (59.9%) 2368 (38.6%) 84 (1.37%)
UK
USA 10 314 6048 (58.6%) 4034 (39.1%) 232 (2.25%)
Data from CAEF report The European Foundry Industry 1996
US data from Modern Castings



Types of cast iron 25
was made by Réaumur in France in 1720. The more useful ‘blackheart’
malleable iron was developed in the USA by Boyden around 1830. Malleable
cast iron became a widely used casting alloy wherever resistance to shock
loading was required. It was particularly suitable for transmission components
for railways and automotive applications.
A major new development occurred in the late 1940s with the discovery
that iron having a nodular form of graphite could be cast directly from the
Figure 2.2 Random flake graphite, 4% picral, ×100. (From BCIRA Broadsheet
138, reproduced by courtesy of CDC.)
Figure 2.3 Malleable cast iron, 4% picral, ×100. (From BCIRA Broadsheet 138,
reproduced by courtesy of CDC.)
26 Foseco Ferrous Foundryman’s Handbook
melt after treatment of liquidiron of suitable composition with magnesium.
(Fig. 2.4). The use of ‘spheroidal graphite’ or ‘nodular’ iron castings has
since grown rapidly as the technology became understood and ‘ductile
iron’, as it is now generally known, has gained a large and still growing,
sector of total cast iron production (Table 2.1).
Figure 2.4 Nodular graphite, 4% picral ×100. (From BCIRA Broadsheet 138,
reproduced by courtesy of CDC.)
The great hardness and abrasion resistance of white iron has also been
exploited. The strength of white iron has been improved through alloying
and heat treatment, and white iron castings are widely used in applications
such as mineral processing, shot blasting etc. where the excellent wear
resistance can be fully used.
Finally there are a number of special cast irons designed to have properties
of heat resistance, or acid resistance etc. In the following chapters, each type
of iron will be considered separately and its method of production described.
The mechanical properties of cast iron are derived mainly from the matrix
and irons are frequently described in terms of their matrix structure, that is,
ferritic or pearlitic:
Ferrite is a Fe–C solid solution in which some Si, Mn, Cu etc. may also
dissolve. It is soft and has relatively low strength. Ferritic irons can be
produced as-cast or by annealing.
Pearlite is a mixture of lamellae of ferrite and Fe3C formed from austenite
by a eutectoid reaction. It is relatively hard and the mechanical properties
of a pearlitic iron are affected by the spacing of the pearlite lamellae,
which is affected by the rate of cooling of the iron from the eutectoid
temperature of around 730°C.
Types of cast iron 27
Ferrite–Pearlite mixed structures are often present in iron castings.
Bainite is usually formed by an austempering heat treatment (normally
on spheroidal graphite irons) and produces high tensile strength with
toughness and good fatigue resistance.
Austenite is retained when iron of high alloy (nickel and chromium) content
cools. Heat and corrosion resistance are characteristics of austenitic irons.
Physical properties of cast irons
The physical properties of cast irons are affected by the amount and form of
the graphite and the microstructure of the matrix. Tables 2.2, 2.3, 2.4, 2.5 and
2.6 show, respectively, the density, electrical resistivity, thermal expansion,
specific heat capacity and thermal conductivity of cast irons. The figures in
the tables should be regarded as approximate.
Table 2.2 Density of cast irons
Grey iron
Tensile strength 150 180 220 260 300 350 400
(N/mm2)
Density at 20°C 7.05 7.10 7.15 7.20 7.25 7.30 7.30
(g/cm3)
Ductile iron
Grade 350/22 400/12 500/7 600/3 700/2
Density at 20°C 7.10 7.10 7.10–7.17 7.17–7.20 7.20
(g/cm3)
Malleable iron
Grade 350/10 450/6 550/4 600/3 700/2
Density at 20°C 7.35 7.30 7.30 7.30 7.30
(g/cm3)
Other cast irons
Type White cast irons Austenitic Grey
Unalloyed 15–30%Cr Ni-Cr (Ni-hard) high-Si (6%)
Density at 20°C 7.6–7.8 7.3–7.5 7.6–7.8 7.4–7.6 6.9–7.2
(g/cm3)
28 Foseco Ferrous Foundryman’s Handbook
Iron casting processes
The majority of repetition iron castings are made in green sand moulds with
resin-bonded cores. The Croning resin shell moulding process is used where
Table 2.3 Electrical resistivity of cast irons
Grey iron
Tensile strength 150 180 220 260 300 350 400
(N/mm2)
Resistivity at 20°C 0.80 0.78 0.76 0.73 0.70 0.67 0.64
(micro-ohms.m2/m)
Ductile iron
Grade 350/22 400/12 500/7 600/3 700/2
Resistivity at 20°C 0.50 0.50 0.51 0.53 0.54
(micro-ohms.m2/m)
Malleable iron
Grade 350/10 450/6 550/4 600/3 700/2
Resistivity at 20°C 0.37 0.40 0.40 0.41 0.41
(micro-ohms.m2/m)
Table 2.4 Coefficient of linear thermal expansion for cast irons
Type of iron Typical coefficient of linear expansion for temperature ranges
(10–6 per °C)
20–100°C 20–200°C 20–300°C 20–400°C 20-500°C
Ferritic flake or nodular 11.2 11.9 12.5 13.0 13.4
Pearlitic flake or nodular 11.1 11.7 12.3 12.8 13.2
Ferritic malleable 12.0 12.5 12.9 13.3 13.7
Pearlitic malleable 11.7 12.2 12.7 13.1 13.5
White iron 8.1 9.5 10.6 11.6 12.5
14–22% Ni austenitic 16.1 17.3 18.3 19.1 19.6
36% Ni austenitic 4.7 7.0 9.2 10.9 12.1
Table 2.5 Specific heat capacity of cast irons
Typical mean values for grey, nodular and malleable irons, from room temperature to 1000°C
Mean value for each temperature range (J/kg.K)
20–100°C 20–200°C 20–300°C 20–400°C 20–500°C 20–600°C 20–700°C 20–800°C 20–900°C 20–1000°C
515 530 550 570 595 625 655 695 705 720
Typical mean values for grey, nodular and malleable irons, for 100°C ranges
Mean value for each temperature range, (J/kg.K)
100–200°C 200–300°C 300–400°C 400–500°C 500–600°C 600–700°C 700–800°C 800–900°C 900–1000°C
540 585 635 690 765 820 995 750 850
Types of cast iron 29
Table 2.6 Thermal conductivity of cast irons
Grey iron
Tensile strength 150 180 220 260 300 350 400
(N/mm2)
Thermal conductivity
(W/m.K)
100°C 65.6 59.5 53.6 50.2 47.7 45.3 45.3
500°C 40.9 40.0 38.9 38.0 37.4 36.7 36.0
Ductile iron
Grade 350/22 400/12 500/7 600/3 700/2
Thermal conductivity
(W/m.K)
100°C 40.2 38.5 36.0 32.9 29.8
500°C 36.0 35.0 33.5 31.6 29.8
Malleable iron
Grade 350/10 450/6 550/4 600/3 700/2
Thermal conductivity
(W/m.K)
100°C 40.4 38.1 35.2 34.3 30.8
500°C 34.6 34.1 32.0 31.4 28.9
high precision and good surface finish are needed. The Lost Foam Process
is also used for repetition castings. Castings made in smaller numbers are
made in chemically bonded sand moulds.
Special sand processes such as Vacuum Moulding and Full-Mould are
used for certain iron castings and there are a few permanent mould (diecasting)
foundries making iron castings, but the short die-life of only a few thousand
components has restricted the use of ferrous diecasting.
Chapter 3
Grey cast iron
Specifications
The properties of grey iron castings are affected by their chemical composition
and the cooling rate of the casting, which is influenced by the section thickness
and shape of the casting. With the widespread acceptance of SI units, there
has been a convergence of national specifications for grey cast iron based on
minimum tensile strength measured in N/mm2 (MPa) on a test piece machined
from a separately cast, 30 mm diameter bar, corresponding to a relevant
wall thickness of 15 mm. There is no requirement in terms of composition
and the foundryman is free to make his own choice based on the requirements
of the particular casting.
In 1997 a European Standard EN 1561:1997 was approved by CEN
(European Committee for Standardization). This standard has been given
the status of a national standard in countries which have CEN members.
CEN members are the national standards bodies of Austria, Belgium, Czech
Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland,
Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,
Switzerland and United Kingdom.
In the UK, for example, the previously used standard BS 1452:1990 has
been withdrawn and replaced by BS EN 1561:1997.
The six ISO grades are generally recognised in most countries. The USA
continues to use grades based on tensile strengths measured in 1000s psi
but now has corresponding metric standards. The data in Table 3.1 is intended
to help foundrymen who are required to supply castings to other countries,
however, it must be understood that while there are similarities between
the various national standards, the grades are not necessarily identical. It is
advisable to consult the original standards for details of methods of testing
etc.
Many specifications also define grades of grey iron specified by their
hardness, related to section thickness. In the European Standard EN 1561:97
Brinell Hardness HB 30 is used, the mandatory values apply to Relevant
Wall Thickness of 40–80 mm (Table 3.2).
An approximate guide to variations in tensile strength with section
thickness is given in Fig. 3.1.
Ta
bl
e 
3.
1
N
at
io
na
l 
st
an
d
ar
d
s
C
ou
n
tr
y
Sp
ec
ifi
ca
ti
on
D
es
ig
na
ti
on
M
in
im
um
 t
ensi
le
 s
tr
en
gt
h 
(N
/
m
m
2 )
10
0
15
0
18
0
20
0
25
0
27
5
30
0
35
0
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0
E
u
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E
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 1
56
1:
19
97
E
N
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0
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0
20
0
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0
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0
35
0
Ja
p
an
JI
S 
G
55
01
 1
99
5
FC
10
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20
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0
30
0
35
0
C
la
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1
2
3
4
5
6
R
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 1
41
2 
19
79
Sc
h
10
15
18
20
25
30
35
40
U
SA
A
ST
M
 A
48
-9
4a
G
ra
d
e
20
25
30
35
40
45
50
60
A
ST
M
 A
48
M
-9
4
G
ra
d
e
15
0
17
5
20
0
22
5
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0
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5
30
0
32
5
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0
In
te
r-
IS
O
 1
85
-1
98
8
G
ra
d
e
10
0
15
0
20
0
25
0
30
0
35
0
na
ti
on
al
E
qu
iv
al
en
t 
to
nf
/
in
2
6.
5
9.
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.2
19
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22
.7
N
ot
e:
 C
on
su
lt
 N
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Sp
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if
ic
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ll 
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32 Foseco Ferrous Foundryman’s Handbook
Relationship between composition, strength and
structure of grey cast iron
The properties of grey irons depend on the size, amount and distribution of
the graphite flakes and on the structure of the metal matrix. These, in turn,
depend on the chemical composition of the iron, in particular its carbon and
silicon content; and also on processing variables such as method of melting,
inoculation practice and the cooling rate of the casting.
Carbon equivalent
The three constituents of cast iron which most affect strength and hardness
are total carbon, silicon and phosphorus. An index known as the ‘carbon
equivalent value’ (CEV) combines the effects of these elements. The grey
iron eutectic occurs at a carbon content of 4.3% in the binary Fe–C system.
If silicon and phosphorus are present, the carbon content of the eutectic is
Table 3.2 HB30 hardness grades of grey iron (EN 1561:1997)
Grade EN-GJL- HB155 HB175 HB195 HB215 HB235 HB255
HB30 min – 100 120 145 165 185
max 155 175 195 215 235 255
Note: Consult EN 1561:1997 for details.
Figure 3.1 Variation of tensile strength with section thickness for several grades of
iron. (Data supplied by CDC.)
Te
ns
ile
 s
tr
en
gt
h 
(N
/m
m
2
)
340
300
260
220
180
140
100
0 20 40 60 80 100 120 140 160 180
Equivalent to 30 mm diameter bar
Cross-section thickness (mm)
Grade 300
Grade 260
Grade 220
Grade 180
Grade 150
Grey cast iron 33
lowered. The effect of Si and P contents on the carbon content of the eutectic
are given by the expression
 
carbon equivalent value (CEV) = T.C.% + Si% + P%
3
Cast irons with carbon equivalent values of less than 4.3% are called hypo-
eutectic irons, those having carbon equivalent values higher than 4.3% are
called hyper-eutectic irons. Since the structure (and hence the strength) of
flake irons is a function of composition, a knowledge of the CEV of an iron
can give an approximate indication of the strength to be expected in any
sound section. This is conveniently expressed in graphical form (Fig. 3.2).
From Fig. 3.2 it is possible to construct a series of curves showing the
reduction of strength with increasing section thickness, this is shown in Fig.
3.1 for the common grades of grey iron. It is important to realise that each
of these curves represents an average figure and a band of uncertainty
exists on either side. Nevertheless, these figures represent those likely to be
achieved on test bars cast in green sand moulds.
Figure 3.2 Relationship between tensile strength and carbon equivalent value for
various bar diameters. (Data supplied by CDC.)
Te
ns
ile
 s
tr
en
gt
h 
(N
/m
m
2 )
350
300
250
200
150
100
CE value
15 mm 20 mm 30 mm
50 mm
75 mm
100 mm
150 mm
5.0 4.5 4.0 3.5
Note that the ‘carbon equivalent liquidus value’ (CEL) is frequently used
as a shop floor method of quality control since it can be directly and readily
measured. When unalloyed molten irons cool, a temperature arrest occurs
when solidification commences, the liquidus arrest. The temperature of this
arrest is related to the C, Si and P content of the iron by the expression
carbon equivalent liquidus (CEL) = T.C.% + Si%/4 + P%/2
The CEL value is a guide to the tensile strength and chilling characteristics
of the iron.
34 Foseco Ferrous Foundryman’s Handbook
Machinability
In general, the higher the hardness, the poorer the machinability and castings
with hardnesses above 250–260 are usually regarded as unsatisfactory. It is
necessary to avoid mottled, chilled or white irons which contain free carbide,
making them hard and unmachinable. Most grey iron castings are required
to be strong and readily machinable, this is achieved with a pearlitic structure
having no free ferrite or free carbide. Soft irons, freely machinable containing
appreciable amounts of free ferrite as well as pearlite, are suitable for certain
applications, particularly for heavy section castings (Fig. 3.3). (Figures 3.1,
3.2, 3.3 are reproduced by kind permission of CDC, Alvechurch, Birmingham.)
Figure 3.3 Relationship between section size, CEV, and structure. (Data supplied
by CDC.)
B
ar
 d
ia
m
et
er
 (
m
m
)
0
5
10
15
20
25
30
35
40
5.0 4.5 4.0 3.5 3.0
CE value
0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
P
la
te
 t
hi
ck
ne
ss
 (
m
m
)
Ferrite and pearlite
(soft and machinable)
Pearlite
(strong and
machinable)
Mottled or white
(hard and unmachinable)
Classification of graphite flake size and shape
The properties of grey iron castings are influenced by the shape and
distribution of the graphite flakes. The standard method of defining graphite
forms is based on the system proposed by the American Society for the
Testing of Metals, ASTM Specification A247 which classifies the form,
distribution and size of the graphite. Certain requirements must be met
Note: The general microstructure of a wide plate is similar to that of a bar with a
diameter equal to twice the thickness of the plate. At a surface however the chilling
tendency of a plate casting will be greater and the structure can then be assumed
to be similar to that of a bar with a diameter equal to the thickness of the plate. The
left-hand scale is therefore used to assess surface chilling tendency and the right-
hand scale for assessing the general structure for a plate casting of a given thickness.
Grey cast iron 35
before a sample is evaluated. Attention must be paid to the location of the
microspecimen in relation to the rest of the casting, to the wall thickness
and the distance from the as-cast surface. Care is also needed in grinding
and polishing so that as much graphite as possible is retained in a
representative cross-section. The specimen is normally examined in the
polished, unetched condition at a magnification of 100× and with a field of
view of about 80 mm.
Flake morphologies are divided into five classes (Fig. 3.4a).
Type A is a random distribution of flakes of uniform size, and is the
preferred type for engineering applications. This type of graphite structure
forms when a high degree of nucleation exists in the liquid iron, promoting
solidification close to the equilibrium graphite eutectic.
Type B graphite forms in a rosette pattern. The eutectic cell size is large
because of the low degree of nucleation. Fine flakes form at the centre of
the rosette because of undercooling, these coarsen as the structure grows.
Figure 3.4 (a) Reference diagrams for the graphite form (Distribution A). The
diagrams show only the outlines and not the structure of the graphite.
Form: I II
III IV
V VI
36 Foseco Ferrous Foundryman’s Handbook
Type C structures occur in hyper-eutectic irons, where the first graphite
to form is primary kish graphite. It may reduce tensile properties and
cause pitting on machined surfaces.
Type D and Type E are fine, undercooled graphites which form in rapidly
cooled irons having insufficient graphite nuclei. Although the fine flakes
Dimensions of the graphite particles forms I to VI
Reference Dimensions of the particles True dimensions
number observed at ×100
(mm) (mm)
1 >100 >1
2 50–100 0.5–1
3 25–50 0.25–0.5
4 12–25 0.12–0.255 6–12 0.06–0.12
6 3–6 0.03–0.06
7 1.5–3 0.015–0.03
8 <1.5 <0.015
Distribution: A
B C
D E
Figure 3.4 (b) Reference diagrams for the distribution of graphite (Form 1). The
diagrams show only the outlines and not the structure of the graphite.
Grey cast iron 37
increase the strength of the eutectic, this morphology is undesirable because
it prevents the formation of a fully pearlitic matrix.
The ASTM Specification also provides standards for measuring flake size.
This is done by comparing a polished microspecimen of the iron at a standard
magnification of 100× with a series of standard diagrams (Fig. 3.4b).
Applications of grey iron castings
Grades of grey iron suitable for various types of casting
Unalloyed grey iron is used for a wide variety of castings. The following
table indicates typical grades of iron used for making certain types of casting.
Table 3.3 is only intended as a guide, casting buyers may specify different
grades from those in the table. Some buyers may have their own specifications
which do not coincide exactly with international or national specifications.
The production of grey irons
In order to produce castings having the required properties, the following
factors must be controlled:
the charge to be melted;
the method of melting;
treatment of the liquid metal before casting.
When deciding on a chemical composition for any casting, the effects of the
main constituents have to be considered. These can be summarised briefly
as follows:
Carbon. The effect of carbon must be considered together with that of
silicon and phosphorus and the concept of carbon equivalent value has
already been discussed. CEV has a major effect on the strength and hardness
of the casting (Figs 3.2, 3.3). CEV also affects the casting properties of the
iron. Irons having CEV below about 3.6% become difficult to cast sound,
because liquid shrinkage occurs and feeding is necessary to achieve complete
soundness.
Silicon. Next in importance to carbon, with regard to the properties of
iron, is silicon. Silicon is a graphitising element, high silicon irons, over
about 1.6%Si, tend to be graphitic, while low silicon irons are mottled or
white. Silicon contents of grey iron are generally around 2.0%.
Manganese. Manganese is necessary to neutralise the effect of sulphur in
38 Foseco Ferrous Foundryman’s Handbook
Table 3.3 Typical grades of grey iron and their use
Class of casting Grade of grey iron used
(tensile strength N/mm2)
Air-cooled cylinders 200–250
Agricultural machinery 200–250
Bearing caps 200
Bearing housings 200
Boilers (central heating) 150–200
Brake cylinders 200
Brake discs 200
Brake drums 200
Clutch housings 200
Clutch plates 200
Cooking utensils 150–200
Counterweights 100–150
Cylinder blocks 200–250
Cylinder heads 200–250
Diesel 250
Electric motor stator cases 200
Drain covers, gulleys, etc. 150
Flywheels 200
Gear boxes 200–250
Ingot moulds 100–150
Lathe beds 100
Machine tool bases 200
Manifolds 200–250
Paper mill drier rolls 150–200
Piano frames 150–200
Rainwater pipes, gutters 150
Refrigerator compressors 250
Tractor axles 150–200
gear boxes 200
Valves, low pressure (gas) 150–200
water 200
hydraulic 250
Water pumps 200
iron. Without sufficient Mn, iron sulphide forms during solidification and
deposits around grain boundaries where it renders the metal hot-short and
likely to produce cracked castings. If sufficient Mn is present, MnS forms as
the molten metal cools and floats out of the metal into the slag layer.
The formula: Mn% = 1.7 × S% + 0.3% represents the amount of Mn
needed to neutralise the sulphur, although the sulphur should not be allowed
to exceed about 0.12%. In addition to combining with sulphur, Mn is a
pearlite stabiliser and it increases the hardness of the iron. However, it is
not primarily used for strengthening because it can affect nucleation adversely.
Mn levels in most irons are typically 0.5–0.8%.
Grey cast iron 39
Sulphur. Sulphur is generally harmful in grey iron, and should be kept to
below 0.12%. Even if the sulphur is adequately neutralised with Mn, if the
high S slag is trapped in the casting, it can cause blowhole defects beneath
the casting skin.
Phosphorus. P has limited solubility in austenite and so segregates during
solidification forming phosphides in the last areas to solidify. While P increases
the fluidity of all cast irons, it makes the production of sound castings more
difficult and the shock resistance of the iron is reduced. For most engineering
castings, phosphorus should be kept below 0.12%, but up to 1.0% may be
allowed to improve the running of thin section castings where high strength
is not required.
Chromium. Added in small amounts, Cr suppresses the formation of free
ferrite and ensures a fully pearlitic structure, so increasing hardness and
tensile strength. Too much Cr causes chill at the edges of the casting, reducing
machinability seriously. Cr up to about 1% may be added to grey irons used
for special purposes, such as camshafts, where chills are often used to create
wear resistant white iron on the cam noses.
In addition to the above elements, the effect of certain impurities in the
iron must also be considered:
Copper. Cu increases tensile strength and hardness by promoting a pearlitic
structure and reducing free ferrite. It reduces the risk of chill in thin sections.
Up to about 0.5% Cu may arise from the presence of Cu as a tramp element
in steel scrap.
Tin. Sn has a similar effect to that of copper, though smaller amounts are
effective. Up to 0.1%Sn ensures a fully pearlitic matrix and reduces free
ferrite. Like copper, small amounts of tin may arise from steel scrap.
Lead. The presence of lead in grey iron, in amounts as low as 0.0004%, can
cause serious loss of strength through its harmful effect on the structure of
flake graphite. Lead contamination in cast iron comes usually through the
inclusion of free-cutting steel in the scrap steel melting charges, though it
can also arise from certain copper alloys such as gun-metal.
Aluminium. Contamination of automotive steel scrap by light alloy
components is the usual source of Al in iron. Levels of 0.1% Al may occur.
Al promotes hydrogen pick-up from sand moulds and may cause pinhole
defects in castings.
Nitrogen. Nitrogen above about 0.01% causes blowholes and fissures in
iron castings, heavy section castings are most seriously affected. Nitrogen
usually arises during cupola melting, particularly if high steel charges are
used, but the use of moulds and cores containing high nitrogen resins can
also cause problems. Addition of 0.02–0.03% titanium neutralises the effect
of nitrogen.
Chapter 4
Melting cast irons
Introduction
Iron foundries require metal of controlled composition and temperature,
supplied at a rate sufficient to match the varying demands of the moulding
line. The metallic charge to be melted consists usually of foundry returns,
iron scrap, steel scrap and pig iron with alloying additions such as ferrosilicon.
The charge is usually melted in a cupola or in an electric induction furnace.
Gas-fired or oil-fired rotary furnaces can also be used, but their use is less
common.
Cupola melting
The cupola (Fig. 4.1) is the classical iron melting unit and is still the most
widely used primary melting unit for iron production due to its simplicity,
reliability and the flexibility in the quality of charge materials that can be
used because some refining of undesirable elements such as zinc and lead
can be achieved. While the cupola is an efficient primary melting unit, it
does not adapt easily to varying demands, nor is it an efficient furnace for
superheating iron. For this reason it is often used in conjunction with an
electric duplexing furnace.
The simplest form is the cold blast cupola which uses ambient temperature
air to burn the coke fuel. The metal temperature that can be achieved is
normally from 1350 to 1450°C but higher temperatures can be achieved
through the use of divided blast (as in Fig. 4.1) or oxygen enrichment.The
refractory linings of cold blast cupolas have a short life of less than 24
hours, so cupolas are operated in pairs, each used alternately while the
other is re-lined.
In hot blast cupolas (Fig. 4.2), the exhaust gases are used to preheat the
blast to 400–600°C, reducing coke consumption and increasing the iron
temperature to more than 1500°C. They may be liningless or use long life
refractories giving an operating campaign life of several weeks.
‘Cokeless’ cupolas (Fig. 4.3), have been developed in which the fuel is
gas or oil with the charge supported on a bed of semi-permanent refractory
spheres. They have advantages of reduced fume emission.
Melting cast irons 41
Cold blast cupola operation
The cupola is charged with:
1. coke, the fuel to melt the iron;
2. limestone, to flux the ash in the coke etc.;
3. metallics, foundry scrap, pig iron, steel and ferroalloys;
4. other additions to improve the operation
Charging
door
Metal and
coke charge
Blast air
Blast air
Slag
Sand bed
Tuyéres
Melting
zone
Iron
Figure 4.1 Section through a cupola (From ETSU Good Practice Case Study 161;
courtesy of the Department of the Environment, Transport and the Regions.)
42 Foseco Ferrous Foundryman’s Handbook
The cupola is blown with air to combust the coke and the air flow controls
the melting rate and metal temperature. The output of a cupola depends
primarily on the diameter of the shaft of the furnace and on the metal/coke
ratio used in the charge. Table 4.1 summarises the operating data for typical
cold blast cupolas.
A useful measure of the efficiency of operation of a cupola is the ‘Specific
Coke Consumption’ (SSC) which is
 
Annual tonnage of coke 1000
Annual tonnage of metallics charged
 = SSC (kg/tonne)
×
This takes into account both charge coke and bed coke. When the cupola is
operated for long enough campaigns, the amount of coke used to form the
bed initially can be ignored. However, as the melting period decreases, the
role of the cupola bed becomes more important. Table 4.2 summarises data
from 36 cupola installations in the UK in 1989. This table provides a useful
reference against which the operation of any cold blast cupola can be
compared.
Coke
The performance of the cupola is highly dependent on the quality of the
coke used. Typical foundry coke has the following properties:
Moisture 5% max.
Ash 10% max.
CUPOLA HEAT EXCHANGER DUST COLLECTOR CHIMNEY
Figure 4.2 Hot blast cupola. (From ETSU Good Practice Case Study 366; courtesy
of the Department of the Environment, Transport and the Regions.)
Melting cast irons 43
Volatiles 1% max.
Sulphur 1% max.
Mean size 100 mm
Undersize <5% below 50 mm
The coke size directly affects coke consumption per tonne of iron melted
and also the melting rate. Optimum cupola performance is achieved with
coke in the size range 75–150 mm, if smaller coke is used, metal temperature
is reduced and a higher blast pressure is needed to deliver the required
amount of air to the cupola. Increasing the size of coke above about 100 mm
has no beneficial effect, probably because large pieces of coke tend to be
fissured and break easily during charging and inside the cupola.
Coke usage in the cold blast cupola is typically 140 kg per tonne of iron
melted (this is an overall figure including bed coke), it is usual to charge
coke at the rate of about 10–12% of the metal charged, but the exact amount
used depends on many factors such as tapping temperature required, melting
rate and the design of the cupola, see Table 4.2.
Charge opening
Air pipe
Blast inlet
Charge
Shell cooling
Ceramic
bedding
Water-cooled grate
Burner
Siphon with slag separator
Carburization
Temperature measuring instrument
Superheater
Deslagging
opening
Tap hole
Inductor
Feeder
Tilting cylinder
Figure 4.3 Schematic diagram of a cokeless cupola in a duplex system.
(From R.F. Taft, The Foundryman, 86, July 1993 p. 241.)
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48 Foseco Ferrous Foundryman’s Handbook
Fluxes
Fluxes are added to the cupola charge to form a fluid slag which may easily
be tapped from the cupola. The slag is made up of coke ash, eroded refractory,
sand adhering to scrap metal and products of oxidation of the metallic charge.
Limestone is normally added to the cupola charge, it calcines to CaO in the
cupola and reacts with the other constituents to form a fluid slag. Dolomite,
calcium–magnesium carbonate, may also be used instead of limestone.
The limestone (or dolomite) should contain a minimum of 96% of CaCO3
(and MgCO3) and should be in the size range 25–75 mm.
The amount of the addition is dependent on the coke quality, the cleanliness
of the charge and the extent of the lining erosion. Normally 3–4% of the
metallic charge weight is used. Too low an addition gives rise to a viscous
slag which is difficult to tap from the furnace. Too high an addition will
cause excessive attack on the refractory lining. When the coke bed is charged,
it is necessary to add around four times the usual charge addition of limestone
to flux the ash from the bed coke.
Other fluxes may also be added such as fluorspar, sodium carbonate or
calcium carbide. Pre-weighed fluxing briquettes, such as BRIX, may also, be
used. BRIX comprises a balanced mixture of fluxing agents which activates
the slag, reduces its viscosity and produces hotter, cleaner reactions in the
cupola. This raises carbon content, reduces sulphur and raises metal
temperature.
Correct additions of flux are essential for the consistent operation of the
cupola and care should be taken to weigh the additions accurately.
The metallic charge
Table 4.3 gives the approximate metal compositions needed for the most
frequently used grades of grey iron. (Data supplied by CDC.)
Table 4.3 Metal composition needed to produce the required grade of grey iron
Grade 150 200 250 300 350
Total carbon (%) 3.1–3.4 3.2–3.4 3.0–3.2 2.9–3.1 3.1 max
Silicon (%) 2.5–2.8 2.0–2.5 1.6–1.9 1.8–2.0 1.4–1.6
Manganese (%) 0.5–0.7 0.6–0.8 0.5–0.7 0.5–0.7 0.6–0.75
Sulphur (%) 0.15 0.15 0.15 max 0.12 max 0.12 max
Phosphorus (%) 0.9–1.2 0.1–0.5 0.3 max 0.01 max 0.10 max
Molybdenum (%) 0.4–0.6 0.3–0.5
Cu or Ni (%) 1.0–1.5
Note: Copper may partially replace nickel as an alloying addition
Metallic charge materials
The usual metallic charge materials are:
Return scrap: runners, risers, scrap castings etc. arising from the foundry
Melting cast irons 49
operation. Care must be taken to segregate each grade of returns if the
foundry makes more than one grade of iron.
Pig iron: being expensive, the minimum amount of pig iron should be
used. Use of pig iron is a convenient way of increasing carbon and silicon
content. Special grades of pig iron having very low levels of residual
elements are available and they are particularly useful for the production
of ductile iron.
Steel scrap: is normally the lowest cost charge metal, it is used for lowering
the total carbon and silicon contents.
Bought scrap iron: care must be taken to ensure that scrap of the correct
quality is used, particularly for the production of the higher strength
grades of iron.
Harmful materials
Care must be taken to ensure that contaminants are not introduced into the
iron. The most common harmful elements are:
Lead, usually from leaded free-cutting steel scrap.
Chromium, from stainless steel.
Aluminium, from aluminium parts in automotive scrap.
Size of metallic charge materials
Thin section steel scrap (below about 5 mm) oxidises rapidly and increases
melting losses. On the other hand, very thick section steel, over 75 mm, may
not be completely melted in the cupola. Metal pieces should be no longer
than one-third of the diameter of the cupola, to avoid ‘scaffolding’ of the
charges.
Ferroalloys
Silicon, manganese, chromium, phosphorus and molybdenum may all be
added in the form of ferroalloys. In some countries, Foseco supplies briquetted
products called CUPOLLOY designed to deliver a specific weight of the
element they introduce, so that weighing is unnecessary.
Ferrosilicon in lump form, containing either 75–80% or 45–50% Si may be
used. Ferromanganese in lump form contains 75–80% Mn. Both must be
accurately weighed before adding to the charge.
Pig irons
Typical pig iron compositions are given in Table 4.4. Refined irons for foundry
50 Foseco Ferrous Foundryman’s Handbook
use are normally made in a hot blast cupola from selected scrap, they may
contain copper, tin, chromium and other alloy elements. Base irons for ductile
(s.g., nodular) iron production are made from specially pure ores, and have
very low residual element contents. They are available in a range of
specifications.
Table 4.4 Foundry pig iron
Grade Typical composition
TC(%) Si(%) Mn(%) S(%) P(%)
Blast furnace irons 3.4–4.5 0.5–4.0 0.7–1.0 0.05 max 0.05 max
Refined irons 3.4–3.6 0.75–3.5 0.3–1.2 0.05 max 0.1 max
Ductile base irons 3.8 0.05–3.0 0.01–0.20 0.02 max 0.04 max
Purchased cast iron scrap is available in a number of grades, typical
compositions are shown in Table 4.5.
Table 4.5 Cast iron scrap
Type Typical composition
TC(%) Si(%) Mn(%) S(%) P(%)
Ingot mould scrap 3.5–3.8 1.4–1.8 0.5–1.0 0.08 0.1
Heavy cast iron scrap 3.1–3.5 2.2–2.8 0.5–0.8 0.15 0.5–1.2
Medium cast iron scrap 3.1–3.5 2.2–2.8 0.5–0.8 0.15 0.5–1.2
Automobile scrap 3.0–3.4 1.8–2.5 0.5–0.8 0.15 0.3 max
Typical charges needed to produce the most frequently used grades of iron
are given in Table 4.6.
Table 4.6 Typical furnace charges
Grade 150 Grade 200 Grade 250
25% pig iron 30% low P pig iron 25% low P pig iron
40% foundry returns 35% foundry return 35% foundry returns
30% bought cast iron 20% low P cast iron scrap 15% low P scrap
5% steel scrap 15% steel scrap 25% steel scrap
Cupola charge calculation
In a normally operated, acid cold blast cupola, the composition of the metal
tapped can be predicted with reasonable accuracy from the composition of
the furnace charge. The tendency is for the total carbon to attain the eutectic
equivalent. If the quantity charged is above this value, a loss may be expected.
On the other hand, where the charge contains less than the eutectic value,
the trend is towards a carbon pick-up. The exact amount of carbon change
must be established by experience for a particular cupola operation, but the
following ‘Levi equation’ is a good starting guide.
Melting cast irons 51
 
TC% at spout = 2.4 + 
TC% in the charge
2
 – 
Si% + P% at spout
4
Silicon is always lost in the cupola, generallya loss of 15% of that charged
may be assumed, but higher losses may occur if high steel charges are used.
Manganese losses are usually about 25%. Phosphorus changes little. Sulphur
always increases due to pick-up from the coke, but the precise amount
cannot be predicted and must be based on experience.
Based on these guide lines, a calculation may be made as follows:
To make a Grade 250 iron with the composition:
TC Si Mn P
3.2 1.7 0.7 0.1
Material Amount Composition Contribution to charge (%)
charged TC Si Mn P TC Si Mn P
(%)
Low-P pig iron 25 3.0 3.0 1.0 0.1 ×0.25 0.75 0.75 0.25 0.03
Grade 250 returns 35 3.2 1.7 0.7 0.1 ×0.35 1.12 0.60 0.25 0.04
Low-P scrap iron 15 3.2 2.2 0.8 0.15 ×0.15 0.48 0.33 0.12 0.02
Steel scrap 25 0.1 0.1 0.3 0.03 ×0.25 0.03 0.03 0.08 –
Ferromanganese 0.3 75 ×0.003 0.23
Total 2.38 1.71 0.93 0.09
Changes during melting Si loss 15% –0.26
Mn loss 25% –0.23
Addition at spout 70% ferrosilicon +0.25
Expected composition T.C. = 2.4 + 2.38/2 – (1.45 + 0.09)/4
 = 3.2
Si = 1.70
Mn = 0.70
P = 0.09
Calculations such as the above example, should only be used as a guide.
The precise carbon pick-up and silicon losses achieved depend on factors
such as coke quality, metal temperature, melting rate etc. Experience will
enable more accurate predictions to be made. A number of computer programs
are available which carry out the calculations rapidly and enable ‘least cost’
charges to be selected.
Cupola output
The maximum output from a cupola is determined primarily by the shaft
diameter, Table 4.1. In normal use, it is necessary to be able to vary the output
to match the requirements of the moulding line. This is done by varying the
blast rate. Increasing or reducing the air supplied to the cupola burns more
or less coke and increases or reduces the melting rate. Unfortunately, changing
the blast rate also changes the temperature of the metal, and to some extent,
52 Foseco Ferrous Foundryman’s Handbook
its composition. This is one of the main drawbacks of the cupola as a melting
furnace. Another problem is that the only way of changing the composition
of the liquid iron is to change the make-up of the charge, and it usually takes
around an hour before the change is seen at the tap-hole. To overcome these
difficuties, it is common practice to tap the cupola into an electric holding
furnace where the temperature and composition can be accurately controlled,
and variations in metal demand can be accommodated.
Emissions from cupolas
Exhaust gases from cupolas are hot and contain dust, grit and SO2 gas. For
many years, the emissions permitted from cold blast cupolas were readily
achieved by the use of simple wet arresters. The cupola gases pass through
a curtain of water which removes the grit particles, absorbs up to half of the
SO2 but does not remove dust. Present day environmental regulations in
most countries impose increasingly strict limitations on the dust emissions
permitted from cupolas, requiring additional dust-arresting plant to be fitted.
Wet scrubbers, bag filters and electrostatic precipitators can be used.
There are two types of wet scrubbers: venturi scrubbers and disintegrators.
Venturi scrubbers rely on the pressure drop across a restricted throat and
disintegrators on the wetting and agglomeration of dust particles by the
action of water carried by a rapidly spinning rotor. Capital cost and running
costs, power and maintenance, are high.
Dry bag filters are capable of achieving lower emission levels than wet
scrubbers. The gases must be cooled before filtration making capital costs
higher than wet scrubbers but running costs may be lower.
Electrostatic precipitators are efficient but are expensive and require
specialised maintenance, they are uncommon on foundry cupolas.
The long campaign hot blast cupola
Hot blast cupolas were, until recently, only considered economical for
foundries with large continuous requirements for molten iron. Hot blast
cupolas are operated on long campaigns, many with unlined, water-cooled
steel shells. Independently fired blast systems have been used but they
have high fuel costs and have now been largely abandoned. There is now
renewed interest in the long campaign hot blast cupola, with recuperative
systems using the heat from combusting the cupola offtake gases to heat the
blast (Fig. 4.2). In part, the change has come about because of environmental
concerns. Cold blast cupolas, in the UK and elsewhere, have in the past
been allowed to operate with simple, low cost emission control. Environmental
controls are now becoming more stringent, requiring high efficiency filtration
of cupola offtake gases. This generally demands combustion then cooling of
the gases prior to filtration. Rather than waste this heat, more foundries are
turning to the hot blast cupola.
Melting cast irons 53
The upper section of the cupola is lined with refractory, while the melting
zone may be liningless (having a water-cooled shell) or it may use a high
quality backing lining with a replaceable inner lining. The liningless cupola
can be operated for several weeks without dropping the bottom. The refractory
lined cupola is usually operated for a week without replacing refractories.
Combustion of the offtake gases is maintained by introducing air into the
shaft below the charging door together with a gas-fired afterburner which
automatically ignites if the temperature of the gases falls too low. The offtake
gases are drawn from the cupola through a recuperator which preheats the
incoming blast air to around 500°C. The blast air is enriched with 1.5–2.0%
oxygen. The waste gases are cooled to 175°C before passing through a dry
bag filter prior to discharge to atmosphere.
Tapping temperatures of 1530°C are achieved. The main savings over
conventional cold blast cupola practice is found in the reduced coke
consumption. Savings of up to 30% of coke usage are claimed. Long campaign
cupolas can be designed for economical operation from 10 tonnes/hr upwards.
The long campaign hot blast cupola is considered by many to be the most
economical method of melting grey iron for foundries.
The cokeless cupola
This is a continuously melting tower furnace in which the metallic charge is
supported on a water-cooled grate on which is a bed of carbonaceous
refractory spheres. Heat for melting is provided by gas (or oil) burners (Fig.
4.3). Superheating of the liquid iron is performed by the heated refractory
spheres and carbon can be added by injecting a suitable recarburiser into
the well of the cupola. Eliminating the coke eliminates sulphur pick-up,
making the cokeless cupola suitable for the production of base iron for
ductile iron production. It also eliminates the main source of atmospheric
pollution. The cokeless cupola retains the advantages of cupola melting:
continuous operation, ability to accept a wide range of raw materials including
wet, oily and contaminated scrap and some refining which removes harmful
elements such as lead and zinc.
The cokeless cupola is particularly attractive in countries where good
quality foundry coke is not available. The most efficient way of using the
cokeless cupola is to tap at around 1350–1400°C into an electric duplexing
furnace where temperature and composition are controlled. This practice
reduces gas consumption to about 55 m3/tonne of metal melted and greatly
reduces the consumption of the refractory spheres of the bed to around
1 kg/tonne of metal melted. Cokeless cupolas with capacity from 5–15
tonnes/h are in use.
Electric melting
Electric melting in the form of arc, induction and resistance furnaces is used
54 Foseco Ferrous Foundryman’s Handbook
increasingly, both for primary melting and holding of liquid iron. Induction
furnaces are the most popular, there are two basic types, the channel furnace
and the coreless induction furnace. Compared with cupola melting, induction
furnaces offer the following advantages:
The ability to produce iron of closely controlled composition.
The ability to control tappingtemperature precisely.
A wide range of charge materials can be used.
Environmental pollution is much reduced.
The stirring effect of induction power rapidly incorporates additions.
The channel furnace
The channel furnace consists of an upper vessel, holding the bulk of the
charge material, with an inductor bolted on the underside (Fig. 4.4).
Figure 4.4 A bath channel induction fumace, showing typical lining arrangement.
(Reproduced by courtesy of CDC.)
Note: High-alumina hot-face
lining may be brick, rammed
or castable refractory
Cover hot-face lining may be
different grade of refractory
from body
Joint High-alumina
hot-face lining Slag port
Rammed or cast
inductor-lining
(high alumina or MgO)
Joint
Throat may be lined in
different grade of
refractory from body
Furnace shell
Alumina-silicate fibre
moist felt next to shell
Insulating blocks or
bricks
All the power is induced within the inductor, heating a loop of molten
metal which transfers its heat to the main body of the charge by convection
and induction forces. The channel furnace will only work providing this
loop is maintained 24 hours per day. The temperature of the metal in the
Melting cast irons 55
loop is higher than that of the metal in the main vessel, which limits the
operating temperature of a channel furnace, since a high loop temperature
shortens the life of the refractory of the loop. This means that their use for
melting is restricted to low temperature metals, such as brass or aluminium.
Channel furnaces are frequently used to duplex iron from a cupola, that is,
the cupola is used as the primary melting unit and continuously delivers
liquid iron to a large (say, 20 tonnes) channel furnace where compositional
variations are corrected and the temperature is maintained at the required
value. This means that the varying demand from the foundry can be met
with metal of precisely the required specification, which cannot be achieved
with a cupola alone.
The disadvantage of the channel furnace is the necessity to operate it for
24 hours per day, and the problems which arise if the refractories of the
induction loop fail.
The coreless induction furnace
In a coreless furnace, the coil surrounds the entire charge (Fig. 4.5). The
mass of refractory is much less than in the channel furnace while the shape
is a simple hollow cylinder. Hence coreless furnaces are much simpler and
Figure 4.5 Section through a coreless induction furnace. (From Jackson, W.W. et
al. (1979) Steelmaking for Steelfounders, SCRATA; reproduced by courtesy of CDC.)
Primary or furnace coil
Charge or secondary coil
Lining
Furnace frame
56 Foseco Ferrous Foundryman’s Handbook
less costly to reline, although they require more frequent relines than the
channel furnace.
The coreless furnace can be designed to operate at any frequency from
50 Hz upwards. Induction heating of liquid metal causes a stirring effect in
the metal. The lower the frequency of the primary current, the more intense
is the stirring. Therefore in a mains frequency furnace operating at 50 or
60 Hz, the turbulence is greater than in one operating at a higher frequency.
Because of the high turbulence, the power input to a mains frequency furnace
is restricted to around 250 kW per tonne of capacity. With higher frequencies,
the power density can be increased to three or four times this level.
The frequency of operation also affects current penetration. The current
induced in the metal charge is a maximum at the surface, reducing at greater
depths. The higher the frequency, the less the effective penetration depth.
This means that at 50 Hz, the smallest ferrous charge piece that can be
efficiently heated is around 450 mm diameter. The smallest practicable furnace
that can hold such a piece is 750 kg in capacity. Mains frequency furnaces
are not effective in sizes smaller than this. On the other hand, at 10 kHz
charge pieces less than 10 mm diameter can be heated, so furnaces as small
as 5 kg capacity can be used.
For most foundry applications, furnaces operating in the range 250–
3000 Hz are used, such furnaces:
allow high power densities giving high melting rates without excessive
stirring;
can be emptied completely after each melt and restarted with virtually
any size of scrap;
have short start-up time and offer flexibility for alloy changes;
allow high production rates from small furnaces;
The development of the solid state inverter in the early 1970s allowed the
possibility of a cheap and reliable form of frequency converter. Silicon
controlled rectifiers (SRCs) convert AC to DC and back to AC at the desired
frequency. Once these had been fully developed, the medium frequency
induction furnace replaced the earlier mains frequency and triple frequency
furnaces. So whereas in the past, choice of frequency was invariably a
compromise because of the limited range possible, now the correct unit for
the application can be supplied. One supplier (Inductotherm) for example,
has supplied:
70 Hz for brass swarf
100 Hz for aluminium scalpings
100–150 Hz for cast iron borings
250 Hz for Al extrusion scrap
250 Hz for iron from foundry returns and steel scrap
500 and 1000 Hz for steel melting and for melting wet cast iron borings
1000 and 3000 Hz for melting a wide variety of copper alloys
3000 Hz for investment casting
10000 Hz for the jewellery trade
Melting cast irons 57
For iron melting furnaces having a melt capacity of around 2–20 tonnes,
frequencies of 200–1000 Hz are usually used, being powered at up to
750 kW per tonne of capacity. Such furnaces normally have a charge-to-tap
time of about 1–2 hours and produce metal at the rate of 2–10 tonnes per
hour.
Energy consumption
A figure of about 500 kWh/tonne is attainable when using a high-powered
medium frequency furnace in a melting role, i.e. when holding periods are
minimised. The energy used can be broken down approximately for a furnace
having the following characteristics (from C.F. Wilford, The Foundryman,
1981 p. 153):
Furnace capacity 4 tonnes
Installed power 3000 kW
Frequency 500 Hz
Standing heat losses (lid on)
averaged over complete melt cycle 47 kW
Power supply efficiency (to furnace coil) 96%
Coil efficiency 80%
Bath diameter 930 mm
Calculated energy consumption
Theoretical energy to melt 4 tonnes of charge to
1500°C 1480 kWh
Energy consumed (allowing for efficiency factors) 1927
Furnace heat losses over one cycle (lid on) 40
Charging time (lid off) 30 min
Extra energy loss incurred with lid off 10
Time for deslagging, temperature measurement
and analysis (lid off) 5 min
Extra energy incurred with lid off 16
Energy consumed to replace lid off losses 34
Total energy consumed (for 4 tonnes) 2001
kWh/t 500
The above figures are theoretical, surveys of actual foundry installations
show that figures of 520–800 kWh/tonne are common, the variation being
due to individual melting practice such as the rate at which the pouring line
will accept molten metal and whether furnace lids are used effectively.
Attention to energy saving measures should allow figures of 550–650 kWh
to be achieved.
58 Foseco Ferrous Foundryman’s Handbook
Charge materials
The maximum dimension of a piece of charge is around one-third of the
crucible diameter. If larger, there is a danger of bridging. The value may be
exceeded when a long piece of charge is fed in a controlled manner into the
crucible. Charge bridging can also be a problem when melting charges of
cast iron borings. It is difficult to generate circulating electric currents in a
cold charge having high electrical resistance between individual pieces (as
found with oxidised borings), so a large sintered mass may form which
does not easily sink down as melting occurs.
An advantage of the medium frequency furnace is that wet charge
components can safely be charged into an empty crucible, eliminating the
necessity of using a charge pre-drying stage. However, care must be taken
not to charge wet material into a fully molten bath.
Alloy recovery
Addition Recovery (%)
Carbon(graphite, petroleum coke) 80–88
Silicon (ferrosilicon 75%) 90
Manganese (ferromanganese 75%) 90–95
Chromium (ferrochromium 60–75%) 90
Molybdenum (ferromolybdenum 60–70%) 90
Nickel 95
Copper 95
Sulphur (iron sulphide) 100
Slag removal
Slag is formed in electric melting furnaces from the products of oxidation of
the elements in the charge, particularly the iron, silicon and manganese;
from refractory erosion and from dirt, sand or rust on the charge. Slag floats
on the surface of the metal and must be removed before tapping. Since slag
removal is an unpleasant task for the furnace operator, it is advisable to
avoid the use of dirty or rusty charge materials. Many slags are liquid and
of low viscosity and difficult to collect, they can be coagulated by adding
SLAX. At molten metal temperatures the SLAX granules expand and form
a low density, high volume crust which mops up the slag, which can then be
lifted off the metal with ease, leaving the surface clean. SLAX is based on
siliceous minerals and reacts with the slag to increase the silica content, and
hence the viscosity. Between 0.07 and 0.2% by weight (0.7–2.0 kg/tonne of
metal) of SLAX 10 or SLAX 30 is scattered over the slag on top of the
furnace. This is rabbled to form a dry, expanded crust and skimmed off.
Melting cast irons 59
Refractories for coreless induction furnaces
Coreless furnaces in iron foundries are usually lined with a silica refractory
bonded with boric acid or, preferably boric oxide. The quality of the silica is
important, it is mined as quartzite and should have the following approximate
composition:
SiO2 Al2O3 Fe2O3 CaO MgO Alkali
98.9% 0.6% 0.2% 0.1% 0.04% 0.2% max
Correct particle sizing is essential so that the lining can be compacted to as
high a density as possible. Typical gradings are:
20% > 1 mm
20% 0.5–1.0 mm
30% 0.1–0.5 mm
30% < 0.1 mm
Boric oxide is usually used as the bonding agent, being mixed by the refractory
supplier. Around 0.7–0.8% B2O3 is used. During the fritting cycle, as the
temperature at the hot face increases, the boric oxide dissolves the silica
fines, producing a borosilicate glass which fills the interstices between the
silica grains and cements them together.
The usual practice with medium frequency furnaces is to coat the copper
coil of the furnace with a layer of ‘mudding’ about 6 mm thick, of a medium
to high alumina cement. This remains in place when the hot face is knocked
out. Between this and the hot face is a layer of ceramic fibre insulation. The
working face is formed by compacting the silica refractory behind a steel
former concentrically placed within the coil. Formers are normally constructed
from mild steel sheet according to the furnace manufacturer ’s design.
Refractory is poured between the former and the coil and compacted using
vibratory ramming tools or manual compaction. Inhalation of silica dust
presents a hazard and respirators should be used during installation or
wrecking of the lining.
The lining is fritted by slow inductive heating of a metallic charge placed
inside the steel former. The heating rate depends on the size of the furnace
and the manufacturer’s recommendations should be followed. In general, a
low heating rate of 50–100°C/h should be used until the temperature reaches
700°C, after which the rate can be increased to 100–200°C/h (the faster rate
being possible with furnaces of size 10 tonnes or less). The temperature
should be raised to 30–50°C above the normal operating temperature of the
furnace, and held for about one hour to complete the fritting operation.
The lining life is very dependent on the particular practice used in the
foundry and the type of iron being melted. For example, the high carbon
and low silicon contents of most ductile base irons, together with the higher
temperatures involved, tends to result in lower lining lives than furnaces
60 Foseco Ferrous Foundryman’s Handbook
used for grey or malleable irons. A 5-tonne furnace melting grey iron should
be capable of melting 600–800 tonnes of iron from one lining, but less than
half this amount if a ductile base iron is being melted.
If a range of irons is melted, requiring higher temperature than normal,
or producing more aggressive slags, it may be necessary to use an alumina
lining. These can be used up to 1750°C and have greater corrosion resistance,
but the cost is much higher. The installed lining cost is around 2.5 times
greater than a silica lining, although the life may be three times longer.
Operating systems
Most iron foundries use two furnace bodies, identical in size, fed from a
single power supply with some means of switching the power supply between
the two furnaces. This allows a continuous supply of molten metal with one
furnace dispensing molten metal while the other is melting the next batch.
Switching techniques have been developed to enable a single power supply
to provide melting power to one furnace while simultaneously providing
holding power to the second so that temperature control can be maintained.
Mechanised charging systems, vibratory conveyors or drop bottom
charging buckets are frequently used to ensure maximum furnace utilisation.
De-slagging is the most arduous and time consuming operation, back tilting
the furnace aids the process.
While most of the ferrosilicon and carburiser are added during furnace
charging, some carbon and silicon losses will occur at high molten metal
temperatures. Trimming additions of 0.2 to 0.3%C and 0.2%Si are typical
during the final stages of the melting process, the stirring action of the
medium frequency power allowing rapid solution and consistent metal
composition.
Fume extraction
Electric melting plant produces less fume than cupola melting, but the ever
increasing stringency of environmental regulations requires fume extraction
plant to be fitted. The charging and pouring operations generate the majority
of the dust and fume emissions within the melt cycle. Close capture fume
hoods or high velocity lip extraction units are specified for fume capture
and dry bag filter systems are sufficient to handle the levels of fume that
arise.
Shop floor control of metal composition
The carbon and silicon content of unalloyed cast irons can be quickly
determined on the shop floor by thermal analysis. A sample of molten iron
Melting cast irons 61
is poured into a small, expendable test mould about 25 mm diameter and 65
mm deep made from resin bonded sand and coated with tellurium to ensure
that the sample freezes white. The test mould also contains a thermocouple
connected to a temperature recorder. As the sample solidifies, the temperature
recorder plots a cooling curve which displays the ‘liquidus arrest’ when the
sample first starts to freeze, then the ‘eutectic arrest’ when freezing is complete.
The liquidus arrest measures the carbon equivalent liquidus value (CEL)
given by:
 
CEL = %C + %Si
4
 + %P
2
Note that CEL is not the same as CEV, %C + (%Si + %P)/3.
The eutectic arrest temperature, on an unalloyed iron of low P%, is a
measure of the silicon content of the iron. Thus from the two arrest
temperatures, the carbon and the silicon content can be calculated. Simple
calculators are available to enable the C% and Si% to be read, or digital
meters are available which display the C% and Si% directly. The carbon
content can be determined with an accuracy of ±0.05%. The silicon
measurement has an accuracy of about ±0.15%
To achieve good results:
the sample must be poured at a high enough temperature to give a well-
defined liquidus arrest. This means that the sampling spoon must be
preheated;
the iron should not be inoculated before testing;
the sample must solidify white.
Special expendable sample moulds are available for the purpose.
Chapter 5
Inoculation of grey cast iron
Introduction
In order to achieve the desired mechanical properties in iron castings, the
liquid iron must have the correct composition and it must also contain
suitable nuclei to induce the correct graphite structureto form on solidification.
The liquid iron must have a suitable ‘graphitisation potential’, this is
determined mainly by its carbon equivalent value, and in particular by the
silicon content. It is normal practice to adjust the graphitisation potential by
controlling the silicon content. However, the effect of other elements must
also be considered. Table 5.1 shows the effect of common alloying elements
relative to silicon for concentrations normally found in practice.
Table 5.1 The graphitising and carbide stabilising effect of
elements relative to Si
Graphitisers Carbide stabilisers
C +3.0 Mn –0.25
Ni +0.3 Mo –0.35
P +1.0 Cr –1.20
Cu +0.3 V –1.0 to 3.0
Al +0.5
From Cast Iron Technology, Elliott, R. (1988), Butterworth-Heinemann,
reproduced by permission of the publishers.
Example: the effect of 1%Al is approximately equivalent to the graphitising
power of 0.5%Si. 1%Cr will neutralise the effect of about 1.2%Si.
Even if iron of the correct chemical analysis is made in the melting furnace,
castings having the desired graphite structure will not be produced without
the addition of inoculants. Inoculants are alloys added in small amounts to
induce eutectic graphite nucleation. Without the presence of suitable nuclei,
liquid iron will ‘undercool’ below the eutectic temperature (Fig. 5.1).
Uninoculated grey iron castings will contain:
undercooled forms of graphite, associated with this will be ferrite;
cementite in thin sections or close to edges and corners.
Such iron is unlikely to meet tensile and hardness specifications and will be
difficult to machine.
Inoculation of grey cast iron 63
There are two main methods of inoculation, ladle and late inoculation. In
the former, the inoculant is added either as the liquid iron enters the ladle
or just afterwards. Late inoculation refers to treatment after the metal has
left the ladle, for example, as it enters the mould (stream inoculation) or by
using an insert in the mould (in-mould inoculation). Inoculants reach
maximum effectiveness immediately after treatment and fade quickly over
a period of 10–20 minutes. It is therefore desirable to inoculate as late as
possible before casting.
Figure 5.1 Graphite structure of (a) uninoculated grey cast iron (×100) and
(b) inoculated grey cast iron (×100). (From BCIRA Broadsheet 161-4; reproduced by
courtesy of CDC.)
(a)
(b)
64 Foseco Ferrous Foundryman’s Handbook
Inoculants are mostly based on graphite, ferrosilicon or calcium silicide,
with ferrosilicon being the most commonly used. Pure ferrosilicon is not
effective as an inoculant, it is the presence of minor elements that determine
the effectiveness of the product. Graphite itself is a powerful inoculant but
it is not effective on low sulphur irons.
Table 5.2 INOCULIN products for inoculation of grey, ductile and compacted
graphite irons
INOCULIN Active Use
product constituents
10 Graphite, alloys containing General grey iron, especially where
Si, Ca, Al, Zr S exceeds 0.08%. Recommended for
max. chill reduction and best graphite
structures in cupola iron. Does not affect
composition of the iron.
25 Ferroalloy containing All types of grey, ductile and CG irons.
65% Si, Ca, Al, Zr and Mn High solubility even in low temperature
metal.
80 Ferroalloy containing 75% Powerful inoculant for grey, ductile
Si, Ca, Zr, Al and CG irons. Good fade resistance.
90 Specially graded Fine powder inoculant for use in
INOCULIN 25 MSI 90 Stream Inoculator.
98 Specially graded Graded for late stream inoculation in
INOCULIN 80 MSI 90 Stream Inoculator.
In addition to the above range of inoculants, Foseco supplies certain
special grades in some countries for particular applications such as low
sulphur irons and for ductile pipe manufacture.
Ladle inoculation
The selected grade of INOCULIN for ladle inoculation should always be
added to the metal stream when tapping from furnace to ladle, or ladle to
ladle. Additions should begin when the ladle is one-quarter full and be
completed when the ladle is three-quarters full, so that the last metal merely
mixes.
Never put INOCULIN into the bottom of the ladle and tap onto it.
The amount of inoculant needed is governed by several factors. The
following rules guide the use of inoculation:
Low carbon equivalent irons require greater amounts of inoculant.
Grey cast irons with less than 0.06% sulphur are difficult to inoculate,
specially formulated products may be required.
For a given iron, the thinner the section of casting, the greater the inoculation
required.
Inoculation of grey cast iron 65
Electric melted irons require more inoculation than cupola melted irons.
Electric melting will also produce low sulphur contents.
High steel scrap charges will require more inoculation.
Where inoculated iron is held for more than a few minutes after inoculation,
there is a need of a higher level of treatment.
It is therefore difficult to give an accurate estimate of the amount of INOCULIN
which is required for every situation. In general, INOCULIN additions of
0.1–0.5% by weight of metal will be satisfactory for grey cast irons, higher
additions are needed for ductile (SG) irons (see p. 79). Care must be taken
not to over-inoculate grey irons, otherwise problems will arise with shrinkage
porosity due to too high a nucleation level. Many grades of INOCULIN
contain high Si content, so that by adding 0.5% of inoculant, the silicon
content of the iron will be raised by as much as 0.3%, this must be allowed
for by adjusting the Si analysis of the furnace metal.
Control methods
The wedge chill test is a simple and rapid method of assessing the degree of
chill reduction obtained by the use of INOCULIN in grey cast irons. Carried
out on the foundry floor, the wedge test is frequently used as a routine
check even when full laboratory facilities are available. The most common
dimensions for the wedge are illustrated in Fig. 5.2.
Figure 5.2 The wedge chill test.
h
b I
t
Base (b) Height (h) Length (I)
mm
6
13
19
25
in
1/4
1/2
3/4
1
mm
11
22
38
57
in
7/16
7/8
11/2
21/4
mm
 57
100
127
127
in
21/4
4
5
5
The wedge is made in a mould prepared from silicate or resin bonded
sand. After pouring, it must be allowed to cool in the mould to a dull red
heat (c. 600°C), after which it can be quenched in water and fractured. The
width at the point where clear chill ceases, t, is measured and this gives a
good indication of the need for inoculation and of the effectiveness of an
66 Foseco Ferrous Foundryman’s Handbook
inoculation process. In general, casting sections should be not less than
three times the wedge reading if chill at the edges and in thin sections is to
be avoided.
After ladle inoculation, the metal must be cast quickly to avoid inoculant
fade.
For certain applications such as continuous casting of iron bar or automatic
pouring of castings, inoculant can be added in the form of filled steel wire
containing INOCULIN 25 which can be fed into a ladle or the pouring basin
of an automatic pouring machine at a computer-controlled rate using the
IMPREX Station (see pp. 73, 78). IMPREX wire is available in a range of
diameters from 6 mm upwards.
Late stream inoculation
With the increasing number of foundries where castings are made on highly
mechanised moulding and pouring lines, the requirements for inoculation
are becoming more difficult to meet. Particular difficulties arise with the
use of automatic pouring furnaces where conventional ladle inoculation is
not possible. A method of carrying out inoculation at the casting stage is
needed and this must be consistent and automatic in operation. The MSI 90
Metal Stream Inoculator is intended for use in these conditions.
It is designed to add controlled amounts of inoculant to the liquid cast
iron just before it enters the mould. The use of late stream inoculation
techniques leads to the virtual elimination of fading. This permits a substantial
reduction in the amount of inoculant used. The inoculant addition thereby
produces a smaller change in iron compositionleading to improved
metallurgical consistency. The cost of inoculation is also lower.
The MSI 90 Stream Inoculator consists of two units, Fig. 5.3, a control unit
and a dispensing unit linked together by a special cable and air line assembly.
The inoculant dispensing cabinet is located in a fixed position over the
mould being poured. A storage hopper for the inoculant is mounted above
the dispensing cabinet. In the latest version, MSI SYSTEM 90-68E, Fig. 5.4,
the flow of inoculant can be regulated either by optical detection of the start
and end of iron flow via an optical module and fibre optic system or by
connecting the system to the pouring furnace electrical signal used to regulate
the flow of liquid iron. The monitoring system checks INOCULIN 90 level,
dispensing tube status, inoculant flow, gate status, compressed air and
dispensing unit temperature. The monitor can automatically interrupt
pouring in the event of malfunction. The control unit is fitted with a printer
port allowing records to be kept. The control cabinet is positioned in a
secure, easily accessible place and may be some distance from the point of
inoculation.
The MSI 90 Stream Inoculator can be operated in conjunction with a
variety of types of pouring equipment:
Inoculation of grey cast iron 67
Low-voltage electricity
cable and air line
Control
unit
Storage hopper for INOCULIN 90
Sensor to detect
metal stream
Ladle
Metal stream
Dispensing unit
controlling flow of inoculant
Delivery tube for INOCULIN 90
to be added to metal stream
Mould
Figure 5.3 The principles involved in the MSI System 90.
Figure 5.4 MSI System 90 Type 68E.
pouring furnaces
ladle transporters
automatic ladle pouring devices
conventional ladles with fixed or variable pouring positions (provided
the latter is within a limited radius).
68 Foseco Ferrous Foundryman’s Handbook
The inoculant used in late stream inoculators must have a number of important
features:
It must be a powerful inoculant.
It must be finely divided to ensure free-flowing properties and rapid
solution.
It must be very accurately graded, without superfine material which
would blow away, or large particles which jam the gate mechanism.
It must dissolve rapidly and cleanly to avoid the presence of undissolved
inoculant particles in the castings.
Sprue
Filter
Runner
Ingate
INOTAB
cast mould
Inoculant
Ratio of cross-sectional areas:
Sprue : Filter : Runner : Ingate
1 : : 1.1 : 1.2
INOTAB and filter application gating
system deslgn
4 : 8 : 3
Conventional gating with INOTAB
cast mould Inoculant
INOTAB cast mould inoculant set in pouring basin
Figure 5.5 Application of INOTAB cast mould inoculant.
Inoculation of grey cast iron 69
These requirements are met by INOCULIN 90, specially developed for this
purpose. INOCULIN 90 is an inoculating grade of ferroalloy containing
balanced proportions of Si, Mn, Al, Ca and Zr, and is an excellent inoculant
for grey and ductile irons. INOCULIN 90 should not be used for normal
ladle inoculation because of its very fine size grading.
Stream inoculation is very efficient since fading is eliminated. The normal
addition rate for grey iron is from 0.03–0.20%, typically 0.1%, much less
than would be used for ladle inoculation. For ductile iron, addition rates
range from 0.06–0.3%, typically 0.2%.
Mould inoculation
There are several ways in which mould inoculation can be performed:
powdered inoculant can be placed in the pouring bush; or it can be placed
at the bottom of the sprue. A more reliable method is to use sachets or
precast slugs of inoculant in the pouring bush or in the running system
(Fig. 5.5).
INOPAK sachets are sealed paper packets containing 5, 10 or 20 g of
graded, fast-dissolving inoculant which can be placed in the runner bush, at
the top of the sprue or in some other situation where there is a reasonable
degree of movement in the metal stream. For most purposes, the addition
rate should be 0.1%, i.e. 5 g of INOPAK for each 5 kg of iron poured.
INOTAB cast mould inoculant tablets are designed to be placed in the
runner where they gradually dissolve in the metal stream as the casting is
poured, giving uniform dissolution. This ensures that inoculation takes place
just before solidification of the iron. Application is simple using core prints
to locate the INOTAB tablet.
INOTAB tablets are normally applied at 0.07–0.15% of the poured weight
of iron. The metal temperature and pouring time of the casting must be
considered when selecting the tablet weight. A minimum pouring temperature
of 1370°C (2500°F) is recommended. It is important that the INOTAB tablet
is located where there is continual metal flow during pouring to ensure
uniform dissolution and the typical application methods are shown in
Fig. 5.5.
Chapter 6
Ductile iron
Production of ductile iron
Ductile iron, also known as spheroidal graphite (s.g.) iron or nodular iron,
is made by treating liquid iron of suitable composition with magnesium
before casting. This promotes the precipitation of graphite in the form of
discrete nodules instead of interconnected flakes (Fig. 2.4). The nodular iron
so formed has high ductility, allowing castings to be used in critical
applications such as:
Crankshafts, steering knuckles, differential carriers, brake callipers, hubs,
brackets, valves, water pipes, pipe fittings and many others.
Ductile iron production now accounts for about 40% of all iron castings and
is still growing.
While a number of elements, such as cerium, calcium and lithium are
known to develop nodular graphite structures in cast iron; magnesium
treatment is always used in practice. The base iron is typically:
TC Si Mn S P
3.7 2.5 0.3 0.01 0.01
having high carbon equivalent value (CEV) and very low sulphur. Sufficient
magnesium is added to the liquid iron to give a residual magnesium content
of about 0.04%, the iron is inoculated and cast. The graphite then precipitates
in the form of spheroids. It is not easy to add magnesium to liquid iron.
Magnesium boils at a low temperature (1090°C), so there is a violent reaction
due to the high vapour pressure of Mg at the treatment temperature causing
violent agitation of the liquid iron and considerable loss of Mg in vapour
form. This gives rise to the familiar brilliant ‘magnesium flare’ during
treatment accompanied by clouds of white magnesium oxide fume. During
Mg treatment, oxides and sulphides are formed in the iron, resulting in
dross formation on the metal surface, this dross must be removed as
completely as possible before casting. It is important to remember that the
residual magnesium in the liquid iron after treatment oxidises continuously
at the metal surface, causing loss of magnesium which may affect the structure
of the graphite spheroids, moreover the dross formed may result in harmful
inclusions in the castings.
Ductile iron 71
Several different methods of adding magnesium have been developed,
with the aim of giving predictable, high yields. Magnesium reacts with
sulphur present in the liquid iron until the residual sulphur is about 0.01%.
Until the sulphur is reduced to near this figure, the magnesium has little
effect on the graphite formation. In the formation of MgS, 0.1%S requires
0.076%Mg. A measure of the true Mg recovery of the treatment process can
be expressed as:
 
Mg recovery % = 
0.76 (S% in base metal – S% residual) + residual Mg%
Mg% added
×
Mg recovery is lower at high treatment temperatures and is dependent on
the particular treatment process used. Magnesium may be added as pure
Mg, or as an alloy, usually Mg–ferrosilicon or nickel–magnesium. Other
materials include briquettes, called NODULANT, formed from granular
mixtures of iron and magnesium and hollow mild steel wire filled with Mg
and other materials.
Magnesium content of treatment materials
Mg–Fe–Si alloy 3–20%
Ni–Mg alloy 5–15%
Mg ingot or wire >99%
Mg–Fe briquettes 5–15%
Cored wire 40–95%
MgFeSi alloys usually also contain 0.3–1.0% cerium accompanied by other
rare earth elements. 0.5–1.0%Cais also a common addition to the treatment
alloy.
Typical analysis of magnesium ferrosilicon nodulariser
Element 5% MgFeSi 10% MgFeSi
Si % 44–48 44 –48
Mg % 5.5–6.6 9.0 –10.0
Ca % 0.2–0.6 0.5 –1.0
RE % 0.4–0.8 0.4 –1.0
Al % 1.2 max 1.2 max
RE (rare earths) contain approximately 50%Ce
Treatment methods include:
Sandwich ladle: the treatment alloy is contained in a recess in the bottom
of a rather tall ladle and covered with steel scrap. The method is suitable
for use only with treatment alloys containing less than 10% Mg (Fig. 6.1a).
Tundish cover: this is a development of the treatment ladle in which a
specially designed cover for the ladle improves Mg recovery and almost
eliminates glare and fume (Fig. 6.1c).
72 Foseco Ferrous Foundryman’s Handbook
Plunger : the alloy is plunged into the ladle using a refractory plunger bell
usually combined with a ladle cover and fume extraction (Fig. 6.1d).
Porous plug: a porous-plug ladle is used to desulphurise the metal with
calcium carbide and the treatment alloy is added later while still agitating
the metal with the porous plug.
Converter: a special converter-ladle is used, containing Mg metal in a
Molten iron Molten iron
Ladle
Ladle
Cover
Alloy
(a) (b)
Treatment
alloy
Metal level
(c) (d)
(b)
Raising and lowering device
Cover
Molten metal
Ladle
Plunging bell
Treatment
alloy
Ductile iron 73
Figure 6.1 Treatment methods for making ductile iron. (a) Sandwich treatment.
(b) Pour-over treatment. (c) Tundish cover ladle. (d) Plunging treatment. (e) GF
Fischer converter. (f) IMPREX cored-wire treatment station (g) In-mould system.
(f)
Stopper
Salamander
plate
Magnesium
chamber
Metal
(e)
Down-sprue
Joint
Inlet
Drag
(g)
Reaction chamber
Runner bar
Cope
Joint
Ingate to
casting
or riser
(cope or drag)
74 Foseco Ferrous Foundryman’s Handbook
pocket. The ladle is filled with liquid iron, sealed and rotated so that the
Mg metal is submerged under the iron (Fig. 6.1e).
Cored wire treatment: wire containing Mg, FeSi, Ca is fed mechanically
into liquid metal in a covered treatment ladle at a special station (Fig.
6.1f).
Treatment in the mould (Inmold): MgFeSi alloy is placed in a chamber moulded
into the running system, the iron is continuously treated as it flows over
the alloy (Fig. 6.1g).
All the methods have advantages and disadvantages; simple treatment
methods can only be used with the more costly low-Mg alloys, generally
containing high silicon levels which can be a restriction since a low Si base
iron must be used. In order to use high Mg alloys and pure Mg, expensive
special purpose equipment is needed so the method tends to be used only
by large foundries.
A survey on ductile iron practice in nearly 80 US foundries in 1988 (AFS
Trans. 97, 1989, p. 79), showed that the biggest change in the previous 10
years was the increase in the use of the tundish ladle, used by over half of
the foundries in the survey. The growth had come at the expense of open-
ladle, plunging, porous plug and sandwich processes. More recently, cored-
wire treatment has been developed and its use is growing.
Melting ductile iron base
While the cupola can be used for the production of ductile iron, the need for
high liquid iron temperatures and close composition control has encouraged
the use either of duplexing with an induction furnace, or using a coreless
induction furnace as prime melter.
In the US survey referred to above, coreless induction furnaces were
used by 84% of the smaller foundries (producing less than 200 t/week).
Almost all larger foundries duplexed iron from an acid cupola to an induction
furnace, with channel furnaces being favourite.
Cupola melting and duplexing
If magnesium treatment with MgFeSi alloy is used, a low Si base iron is
needed. The process may be summarised as follows:
Melt in acid cupola, charge foundry returns and steel scrap plus low
sulphur pig iron if necessary.
Tap at around 2.8–3.2%C
0.6–1.0%Si
0.08–0.12%S
Ductile iron 75
Desulphurise, using porous plug treatment with calcium carbide, to about
0.10%S, carburise to 3.6–3.8%C.
Transfer to induction furnace, adjust C and Si and temperature to required
levels.
Treat with MgFeSi and inoculate.
Cast.
Induction furnace melting
Charge foundry returns, steel scrap, ferrosilicon and carburiser to achieve
the desired composition.
If sulphur is below 0.025%, desulphurisation is not necessary, but the
higher the sulphur content, the more magnesium must be used so the
cost of treatment increases.
Treat with Mg and inoculate.
Cast.
If a converter or cored-wire Mg treatment is used, high silicon base irons are
satisfactory. Separate desulphurisation is not necessary since, with these
processes it is economical to use pure magnesium as a desulphuriser.
Use of the tundish cover ladle
The most commonly used treatment method, particularly in smaller foundries
is the tundish covered treatment ladle. The principle is shown in Fig. 6.1c.
The use of a refractory dividing wall to form an alloy pocket in the bottom
of the ladle gives improved Mg recovery compared to a pocket recessed in
the bottom of the ladle. Treatment batches are usually in the range, 450–
1000 kg. Figure 6.2 shows the design of a ladle suitable for the treatment of
about 450–500 kg of iron. The diameter of the filling hole is chosen to minimise
the generation of fume while allowing the ladle to be filled quickly without
excessive temperature loss. It is essential that the MgFeSi alloy is not exposed
to the liquid iron until quite late in the filling procedure, so the filling hole
is positioned to introduce liquid iron away from the alloy pocket in the
ladle bottom. The Mg alloy in the alloy pocket is covered with steel turnings
or FeSi pieces of size 25 × 6 mm, then when the level in the ladle reaches the
dividing wall, iron flows over and forms a semi-solid mass with the cover
material allowing the ladle to be almost filled before the reaction starts, thus
ensuring good recovery of Mg.
In order to minimise temperature losses during treatment, the ladle and
cover should be separately heated with gas burners before assembly.
Immediately before use, the ladle should be filled with base iron from the
melting furnace and allowed to soak for a few minutes before returning the
iron to the furnace. The prescribed weight of MgFeSi alloy is charged through
76 Foseco Ferrous Foundryman’s Handbook
the alloy charging tube which is plugged after removal of the charging
funnel. The treatment alloy may be any of the MgFeSi alloys with Mg in the
range 3–6%, additions of 1.5–3.0% are made giving Mg additions of 0.08–
0.15%. Tapping time is usually around 40 seconds.
The temperature loss during treatment is around 50°C, so the tapping
temperature must be adjusted accordingly, treatment temperatures of around
1530°C are commonly used. After treatment, the tundish cover is removed,
the metal transferred to a pouring ladle where inoculation may take place,
then it is cast.
Figure 6.2 Plan and cross-section of tundish/cover Iadle. (From Anderson, J.V.
and Benn, D. (1982) AFS Trans, 90, 159–162.)
Alloy feed pipe φ = 75 mm
(removable cap)
φ 38 mm
20
3 
m
m
584
24
1
10
0
61
0
All dimensions in mm
20
3
φ = 444
Liquid iron level at 1000 lbs
(455 kg)
Cover material
MgFeSi alloy
Ductile iron 77
Sandwich treatment
A popular method of treatment, frequently used in smaller foundries, is the
sandwich method (Fig. 6.1a). This is essentially the same as the tundish-
cover method but carried out in an open ladle. The magnesium alloy is
placed in a pocket in the bottom of the ladle and covered with steel scrap
(2–3% of the metal weight) or a steel plate. The molten metal stream is
directed away from the pocket. The pocket must be deep enough to contain
all the alloy and the steel scrap which should be of small size to produce a
high packing density. The treatment ladle is usually deep, with a height-to-
diameter ratio of 1.5–2.0 :1, the extra metal depth increases the recovery of
the magnesium, whichcan be as high as 50% when a 5%Mg alloy is used.
NODULANT
NODULANT briquettes are essentially formed of pure magnesium and
sponge iron. They contain 10% Mg and minor quantities of calcium, cerium,
silicon and carbon. The briquettes weigh between 16 and 20 g and have a
density of 4.3–4.5 g/ml, so they are suitable for use in the sandwich or
tundish cover technique in just the same way that MgFeSi is used. Magnesium
yields are around 40%. The major advantage of using NODULANT is that
a negligible amount of silicon is added during the treatment. This permits
the use of higher silicon in the base iron enabling all the available ductile
iron returns to be used in the charge. By increasing the base silicon, the
lining life of the induction furnace is increased by as much as 40%.
Pure magnesium converter process
The Georg Fischer converter (Fig. 6.1e), has a reaction chamber formed by
a graphite-clay plate of semi-circular section set into the lining of the converter.
Molten iron is charged with the converter in the horizontal position. The
reaction chamber is charged with pure Mg lumps and other additives (if
required) and sealed with a locking stopper. The converter spout is closed
by a pneumatically operated lid. The vessel is then tilted to vertical allowing
a limited amount of metal to enter through holes in the chamber and react
with the magnesium which starts to vaporise. The vapour pressure in the
reaction chamber rises slowing the further entry of liquid iron and allowing
controlled treatment of the contents of the converter. Treatment takes 60–90
seconds. The melt is first deoxidised then desulphurised. When the sulphur
content has dropped to less than 0.002%, the melt starts to absorb magnesium.
Magnesium recovery can be as high as 70%. Base irons with high sulphur
contents of 0.2–0.3%S can be used because of the high efficiency of Mg use.
The standard converter allows up to 2.5 tonnes of iron to be treated 6–8
78 Foseco Ferrous Foundryman’s Handbook
times per hour. Larger units with capacity up to 10 tonnes are available. The
reaction chamber wall has a limited life of 200–800 treatments. Temperature
loss is 22–33°C in a 1-tonne converter but less in larger converters. Since no
Si is added during treatment, an unlimited amount of ductile iron returns
can be used.
The process is operated under licence from Disa Georg Fischer.
Cored-wire treatment
The equipment and principle of the method is shown in Fig. 6.1f which
shows the Foseco IMPREX-Station. The treatment station consists of a coil
of hollow mild steel tube filled with Mg metal, a feeding machine, a guide
tube and a ladle with a close fitting lid. On entering the molten metal, the
sheathing of the wire dissolves releasing the core material below the metal
surface. Wires vary in size from 4 mm to 13 mm. The amount of wire needed
is dependent on the sulphur content of the base iron, the temperature of the
iron and the reactivity of the wire used. Once the treatment parameters
have been established, it is a simple matter to calculate the amount of
wire required and the treatment time. Feed details can then be programmed
into a computer. Typical feed rates of 9 mm wire are 30–50 metres per
minute. 1500 kg of metal can be treated in about 2 minutes. Treatment
temperature starts at around 1450°C, dropping to around 1410°C at the
finish.
In-the-mould treatment
It is possible to carry out the nodularising treatment in the mould by
incorporating a specially designed magnesium treatment chamber in the
gating system into which the treatment alloy is placed (Fig. 6.1g). The gating
method must fill with metal as quickly as possible and must maintain constant
flow conditions so that all the metal, from first to last, is equally treated.
Since treatment of iron with Mg always produces some MgO and MgS
dross, care must also be taken to avoid dross entering the casting. This is not
easy to achieve and requires a good deal of experimentation so the method
is generally only used by large repetition foundries, which are able to devote
considerable time to solving the process problems.
Inhibiting elements
Certain elements which may be present in the base iron have an inhibit-
ing effect on nodule formation, the following elements are known to be
harmful:
Ductile iron 79
Aluminium above 0.13%
Arsenic above 0.09%
Bismuth above 0.002%
Lead above 0.005%
Tin above 0.04%
Titanium above 0.04%
Antimony, tellurium and selenium are also harmful. The combined effect of
two or more of these elements may be even more harmful. The addition of
cerium and other rare earth elements, together with calcium will neutralise
many of the harmful effects of inhibiting elements and most MgFeSi
nodularising alloys contain 0.3–1.0% Ce and other rare earths. 0.5–1.0% Ca
is also commonly present.
Inoculation and fading
Immediately after treatment, the iron must be inoculated. Larger additions
of inoculant are needed compared with grey iron and from 0.5–0.75% of a
graphitising inoculant such as INOCULIN 25 should be used. Inoculation
treatment is not permanent, the effect begins to fade from the time the
inoculant is added. As the inoculating effect fades, the number of nodules
formed decreases and the tendency to produce chill and mottle increases. In
addition the quality of the graphite nodules deteriorates and quasi-flake
nodules may occur.
When inoculating ductile iron, the inoculant must be added after the
magnesium flare has subsided. A common practice is to tap about half the
metal onto the magnesium alloy and wait for the flare to finish before adding
the inoculant to the tapping stream as the rest of the metal is tapped. If the
metal is transferred from the treatment ladle to a casting ladle, an effective
practice is to make a further small addition of inoculant as the metal is
poured into the casting ladle. About 0.1–0.2% of inoculant is adequate.
Significant fading occurs within five minutes of inoculation. Because of
this problem, late stream or mould inoculation is commonly used in ductile
iron production, see p. 68.
Specifications for ductile cast iron
Table 6.1 lists a number of national and international specifications for ductile
iron, it is necessary to consult the original specifications for details of the
methods of testing and the mandatory values that must be achieved. In
recent years, specifications in different countries have been converging so
they are now all quite similar. Table 6.2 lists the suggested chemical
compositions required to produce castings that meet the specifications in
the as-cast state.
Ta
bl
e 
6.
1
Sp
ec
if
ic
at
io
ns
 f
or
 d
u
ct
ile
 (
no
d
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la
r)
 c
as
t 
ir
on
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ou
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ry
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in
im
um
 t
en
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le
 s
tr
en
gt
h/
el
on
ga
ti
on
Sp
ec
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ca
ti
on
(N
/
m
m
2 /
%
)
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ro
p
e 
E
N
-G
JS
-
35
0-
22
40
0-
18
40
0-
15
45
0-
10
50
0-
7
60
0-
3
70
0-
2
80
0-
2
90
0-
2
C
E
N
 1
56
3:
19
97
U
K
*
B
S2
78
9
35
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22
40
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18
42
0/
12
45
0/
10
50
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7
60
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3
70
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2
80
0/
2
90
0/
2
19
85
U
SA
 A
ST
M
 A
53
6
60
-4
0-
18
60
-4
2-
10
65
-4
5-
12
70
-5
0-
05
80
-5
5-
06
80
-6
0-
03
10
0-
70
-0
3
12
0-
90
-0
2
19
93
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p
an
 J
IS
 F
C
D
35
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40
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18
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45
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0-
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G
55
02
19
95
In
te
r-
IS
O
 1
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3
35
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7
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0-
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90
0-
2
na
ti
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al
 1
98
7
H
ar
d
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ss
Ty
p
ic
al
 H
B
<
16
0
13
0-
17
5
13
5-
18
0
16
0-
21
0
17
0-
23
0
19
0-
27
0
22
5-
30
5
24
5-
33
5
27
0-
36
0
Ty
p
ic
al
F
F
F
F 
&
 P
F 
&
 P
F 
&
 P
P
P
 o
r 
T
T
M
st
ru
ct
u
re
s
N
ot
es
:
T
he
 E
u
ro
p
ea
n 
C
E
N
 1
56
3 
St
an
d
ar
d
 a
ls
o 
sp
ec
if
ie
s
35
0-
22
-L
T
 a
nd
 4
00
-1
8-
LT
 f
or
 l
ow
 t
em
p
er
at
u
re
s.
35
0-
22
-R
T
 a
nd
 4
00
-1
8-
R
T
 f
or
 r
oo
m
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em
p
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re
.
*B
S2
78
9 
ha
s 
be
en
 w
it
hd
ra
w
n 
an
d
 r
ep
la
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 b
y 
E
N
15
63
:1
99
7.
T
he
 d
es
ig
na
ti
on
s 
of
 U
S 
St
an
d
ar
d
s 
e.
g.
 1
00
-7
0-
03
, r
ef
er
s 
to
 m
in
. t
en
si
le
 s
tr
en
gt
h(
lb
f/
in
2 )
-m
in
. p
ro
of
 s
tr
es
s-
el
on
ga
ti
on
 %
.
T
he
 s
tr
u
ct
u
re
s 
ar
e:
 T
M
, t
em
p
er
ed
 m
ar
te
ns
it
e;
 P
 o
r 
T,
 p
ea
rl
it
e 
or
 t
em
p
er
ed
 s
tr
u
ct
u
re
; P
 &
 F
, p
ea
rl
it
e 
an
d
 f
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ri
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; F
, f
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ri
te
.
T
hi
s 
Ta
bl
e 
is
 i
nt
en
d
ed
 o
nl
y 
as
 a
 g
u
id
e,
 r
ef
er
 t
o 
th
e 
N
at
io
na
l 
St
an
d
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s 
fo
r 
d
et
ai
ls
.
Ta
bl
e 
6.
2
Su
gg
es
te
d
 a
na
ly
se
s 
fo
r 
as
-c
as
t 
p
ro
d
u
ct
io
n 
of
 d
u
ct
ile
 i
ro
n
A
ve
ra
ge
G
ra
de
s
G
ra
de
G
ra
de
G
ra
de
ca
st
in
g
80
0/
2,
70
0/
2,
60
0/
3
50
0/
7
40
0/
12
40
0/
18
se
ct
io
n
T
C
Si
M
n(
m
ax
)
T
C
Si
M
n(
m
ax
)
T
C
Si
M
n(
m
ax
)
T
C
Si
M
n(
m
ax
)
<
13
 m
m
3.
6–
3.
8
2.
6–
2.
8
0.
5
3.
6–
3.
8
2.
6–
2.
8
0.
3
3.
6–
3.
8
2.
6–
2.
8
0.
2
3.
6–
3.
8
2.
6–
2.
8
0.
1
13
–2
5
3.
5–
3.
6
2.
2–
2.
5
0.
6
3.
5–
3.
6
2.
2–
2.
5
0.
35
3.
5–
3.
6
2.
2–
2.
4
0.
25
3.
5–
3.
6
2.
2–
2.
4
0.
15
25
–5
0
3.
5–
3.
6
2.
1–
2.
3
0.
7
3.
5–
3.
6
2.
1–
2.
4
0.
4
3.
5–
3.
6
2.
2–
2.
4
0.
3
3.
5–
3.
6
2.
2–
2.
4
0.
20
50
–1
00
3.
4–
3.
5
1.
9–
2.
1
0.
8
3.
4–
3.
5
2.
0–
2.
2
0.
5
3.
4–
3.
5
2.
0–
2.
2
0.
35
3.
4–
3.
5
1.
8–
2.
0
0.
2
>
10
0
3.
4–
3.
5
1.
8–
2.
0
0.
8
3.
4–
3.
5
1.
8–
2.
0
0.
6
3.
4–
3.
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1.
8–
2.
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N
ot
es
: F
or
 t
he
 h
ig
he
r 
st
re
ng
th
 g
ra
d
es
, 8
00
,7
00
,6
00
, a
d
d
it
io
ns
 o
f 
0.
5%
 C
u
 o
r 
0.
1%
 S
n 
m
ay
 b
e 
m
ad
e 
to
 e
nc
ou
ra
ge
 p
ea
rl
it
e 
fo
rm
at
io
n.
In
 a
ll 
gr
ad
es
:
P
ho
sp
ho
ru
s 
sh
ou
ld
 b
e 
le
ss
 t
ha
n 
0.
05
%
C
hr
om
iu
m
 s
ho
u
ld
 b
e 
le
ss
 t
ha
n 
0.
05
%
R
es
id
u
al
 M
g 
sh
ou
ld
 b
e 
0.
03
–0
.0
6%
82 Foseco Ferrous Foundryman’s Handbook
Heat treatment of ductile iron
It is obviously desirable to achieve the required properties in the as-cast
form, but this is not always possible because of variations of section thickness
etc. Heat treatment of the castings will eliminate carbides in thin sections,
produce more consistent matrix structures and for a given structure, the
mechanical properties are often improved by heat treatment, especially by
normalising. Where tempered martensite structures are needed, heat treatment
is essential.
Stress relief
Heat at 50–100°C/h to 600°C (taking care not to exceed 610°C), soak for one
hour plus an hour for every 25 mm of section thickness in the thickest
section. Cool at 50–100°C/h to 200°C or less. Ensure that the castings are
adequately supported in the furnace so that they are not subjected to stress.
Breakdown of carbides
Thin section castings may contain carbides in the as-cast structure, these
can be eliminated by soaking the castings at 900–925°C for 3 to 5 hours.
Annealing to produce a ferritic matrix
Castings should be soaked at 900–925°C for 3–5 hours, followed by slow
cooling at around 20–35°C/h through the critical temperature (about 800–
710°C), then furnace cooled at, say 50–100°C/h to 200°C.
Normalising to produce a pearlitic matrix
Soak the castings above the critical temperature then air cool. Again a soaking
temperature of 900–925°C is usually used, to ensure that carbides are broken
down, then use forced air cooling to form pearlite. The type of heat treatment
furnace available and the size of the load determines the cycle that is possible.
It may be necessary to adjust the metal composition with tin or copper to
help the formation of fully pearlitic structures.
Hardened and tempered structures
Austenitise at 900–920°C then oil quench. Tempering is usually carried out
at 600–650°C.
Ductile iron 83
Austempered ductile iron (ADI)
Austempering is an isothermal heat treatment for producing ‘bainitic’
structures. It can double the strength of ductile iron while retaining good
ductility and toughness. Wear resistance and fatigue properties are excellent
so that ADI is comparable with wrought steel.
The ADI heat treatment is a two-stage process, shown in Fig. 6.3.
Austenitising is carried out at 815–930°C to fully transform the matrix to
austenite. This is done either in a non-oxidising atmosphere furnace or in a
high temperature salt bath, temperatures and times are determined by
chemical composition, section size and grade of ADI required. 1 to 1.5 hours
is usually adequate. Slow initial heating of the casting is desirable to avoid
the danger of cracking of complex shapes. The castings are then quenched
to the required isothermal heat treatment temperature, usually between 210
and 400°C. This is usually done in a salt bath (Fig. 6.3). The castings are held
at temperature for 1–2 hours to complete the transformation of austenite to
bainite. The lower temperatures give high hardness, strength and wear
resistance, while the higher heat treatment temperatures result in higher
ductility and toughness. After the isothermal treatment, the castings are
cooled to ambient temperature.
Unalloyed ductile irons may be austempered in sections up to about
8 mm. Thicker section castings require the addition of Mo or Ni to increase
the hardenability.
Typical changes in properties due to austempering of an unalloyed iron are:
As-cast Austempered 1h Austempered 1h
at 300°C at 375°C
Tensile strength (N/mm2) 475 1465 1105
Elongation (%) 19 1 9
Hardness (HB) 160 450 320
Austempered ductile iron finds applications as a replacement for forged
steel components in the agricultural, mining, automotive and general
engineering industries; for example: plough tips, digger teeth, spring brackets,
rear axle brackets, gears etc. ADI production is growing but its use is limited
to some extent by the lack of suitable heat-treatment facilities.
The European/British Specification BS EN 1564:1997 defines four grades
of ADI, Table 6.3.
Table 6.3 European grades of ADI
Material designation Tensile 0.2%PS Elongation Hardness
strength (MPa) (MPa) (%) (HB)
EN-GJS-800-8 800 500 8 260–320
EN-GJS-1000-5 1000 700 5 300–360
EN-GJS-1200-2 1200 850 2 340–440
EN-GJS-1400-1 1400 1100 1 380–480
84 Foseco Ferrous Foundryman’s Handbook
Mechanical properties are measured on test pieces machined from
separately cast test pieces.
In North America, the ASTM has defined five standard grades of ADI,
Table 6.4.
Table 6.4 The five ASTM standard ADI grades (ASTM A897M-90)
Grade TensiIe* Yield* Elongation* Impact Typical
strength strength (%) energy* hardness
(MPa) (MPa) (Joules) (BHN)
1 850 550 10 100 269–321
2 1050 700 7 80 302–363
3 1200 850 4 60 341–444
4 1400 1100 1 35 388–477
5 1600 1300 N/A N/A 444–555
*Minimum values
Casting ductile iron
Ductile iron differs from grey iron in its casting characteristics in two important
respects. Unlike grey iron, ductile iron is a dross-forming alloy. The residual
magnesium which is needed to ensure nodular graphite formation rapidly
oxidises whenever the liquid metal is exposed to air; in the ladle, during
metal transfer and in the mould. A magnesium silicate dross is formed
which may give rise to defects at or just below the casting surface, usually
on the upper surfaces of the castings. For this reason, it is common practice
to filter ductile iron castings through ceramic filters, see Chapter 18.
The other major difference compared with grey iron, is the need to feed
ductile iron castings to ensure freedom from shrinkage defects. Ductile irons
always have a high carbon equivalent so the volume of graphite precipitated
during solidification should ensure completely sound sections. However,
the expansion resulting from the graphite precipitation results in large
pressures being exerted on the mould walls, much higher than those found
with grey iron(figures of 1000–1500 kPa or 145–217 lbf/in2 have been
measured compared with 170–200 kPa or 24–29 lbf/in2 in grey iron). Only
the strongest moulds, such as sodium silicate bonded moulds or well-vibrated
lost foam moulds, will resist such pressures so the use of feeders is common
when ductile iron castings are made.
Compacted graphite irons
Compacted graphite (CG) irons are a range of cast irons having mechanical
properties intermediate between those of grey and ductile irons. Under the
microscope the graphite appears as short, thick flakes with rounded ends,
readily distinguished from true flake graphite (Fig. 6.4). Compacted graphite
Ductile iron 85
is interconnected in a branched structure, and is more like flakes than the
completely isolated nodules in ductile iron. Compacted graphite is not the
same as vermicular graphite which can occur in irons of very low sulphur.
Compacted graphite iron has good casting characteristics, due to its high
fluidity and low solidification shrinkage. The tensile, yield and fatigue
strengths of CG iron are 1.5–2 times that of grey iron, approaching ductile
iron. Thermal conductivity is comparable with grey iron and machinability
1000
800
600
400
200
Te
m
pe
ra
tu
re
 °
C
0 1 2 3 4 5 6 7 8
Time hr
Typical austempering heat treatment stages
Grade 4
AD1
Grade 1
AD1
930°C
815°C
400°C
(260–320 BHN)
230 °C
21/2 hr max
(400–500 BHN)
Figure 6.3 Typical austempering heat-treatment stages. (R.D. Forrest, 13th DISA/
GF Licensee Conference 1997. Courtesy Rio Tinto Iron and Titanium GmbH.)
Figure 6.4 Structure of compacted graphite. (Courtesy SinterCast.)
CGI microstructure100 µm
86 Foseco Ferrous Foundryman’s Handbook
is intermediate between grey and ductile irons of similar matrix structures.
This combination of properties makes CG iron suitable for upgrading of
castings traditionally produced of grey iron.
Production of compacted graphite iron
There are several methods by which compacted graphite may be produced:
Cerium additions
Magnesium additions
Nitrogen additions
Magnesium plus titanium additions
One method involves the joint addition of a nodularising and a de-
nodularising agent, usually magnesium and titanium often with a small
cerium addition as well. Special treatment alloys have been developed for
the production of CG iron.
Mg Ti Ce Ca Al Si Fe
4.5–5.5 8.0–10.0 0.3–0.4 1.0 max 1.5 max 50–54 balance
As with ductile iron, it is desirable to start with a low sulphur iron, below
0.02%. The base iron for treatment is best melted in an induction furnace
and should have composition in the range:
CE C Si Mn S P
3.7–4.5 3.1–3.9 1.7–2.9 0.1–0.6 0.035 max 0.06 max
A sandwich technique may be used with addition rates between 0.6–1.6%
depending on the foundry conditions. The treatment temperature should
be above 1350°C to avoid the formation of a fully nodular structure. Inoculation
of the treated iron is necessary and additions of 0.2–0.5% ferrosilicon are
common. The matrix structure may be made ferritic or pearlitic as with
ductile iron. Titanium-containing alloys can cause problems due to build-
up of Ti in foundry returns leading to impaired machinability.
The use of compacted graphite iron was limited for many years by the
difficulty foundries experienced in controlling the process within the narrow
range of CGI stability so it was considered an unreliable material.
A Swedish company, SinterCast, has developed a method of process
control for CGI which allows CGI to be made reliably. The process can be
licensed by foundries. Figure 6.5 represents the transition of graphite
morphology from flake to compacted and ultimately to spheroidal graphite
as a function of Mg content. This suggests that a range of 0.005–0.010% total
Mg will cause formation of compacted graphite. This curve does not fully
account for reactions between Mg and dissolved elements in the iron,
particularly oxygen and sulphur. Figure 6.6 illustrates by deep etched scanning
Ductile iron 87
Figure 6.6 The transition of graphite morphology from flake to compacted to
spheroidal shown by deep etched scanning electron micrographs.
(Courtesy SinterCast.)
Grey iron to ductile iron transition
Ductile iron
100
80
60
40
20
0
%
 N
od
ul
ar
ity
CGI
Grey
0.010 0.020 0.030 0.040 % Total Mg
Figure 6.5 The effect of total Mg content on the transformation of graphite morphology
from flake to compacted and ultimately to spheroidal graphite. (Courtesy SinterCast.)
electron micrographs, the transition of graphite morphology from flake to
compacted to spheroidal. The SinterCast Process involves taking a sample
of liquid iron from the ladle in a patented sampling cup and carrying out a
thermal analysis using two thermocouples, one in the centre of the cup and
the other adjacent to the wall. The two cooling curves allow the degree of
modification and inoculation required to be determined. Independent
additions of cored wire containing Mg and inoculant are then made to the
ladle. Ladle to ladle variations in the oxygen and sulphur content of the iron
are thus allowed for and reliable compacted graphite iron is made.
88 Foseco Ferrous Foundryman’s Handbook
Foundry properties of compacted graphite iron
The fluidity is governed by carbon equivalent (CE) and temperature and is
similar to grey or ductile irons of the same CE. Because CG irons are stronger
than grey irons, a higher CE can be used to obtain the same strength, this
allows greater fluidity and easier running of thin sections. CG iron is dross-
forming, just as ductile iron, and filtration of castings is desirable. CG irons
are more prone to chill than grey irons but less likely to chill than ductile
iron. Good inoculation is necessary. Fading occurs, but to a smaller extent
than in ductile iron, but excessive delays between treatment, inoculation
and casting should be avoided.
There is some disagreement about the level of feeding required for CG
iron. There is less tendency for mould wall movement than with ductile
iron, nevertheless some feeding appears to be desirable.
Applications of compacted graphite irons
There has been great interest in its use for automotive castings such as
diesel cylinder blocks and heads, hydraulic components, exhaust manifolds,
brake drums, brake discs, flywheels etc. The lack of consistency of properties
held back the wide scale application of CG iron but with the greater control
now possible its use is expected to develop.
Properties of compacted graphite irons
Table 6.5 Comparison of CG iron properties with grey and ductile irons
Property Grey irons CG irons Ductile irons
Tensile strength
ton/in2 11–20 20–38 26–45
lb/in2 25–45 000 45–85 000 60–100 000
kg/mm2 16–32 30–60 40–70
N/mm2 160–320 300–600 400–700
Elongation (%) nil 3–6 6–25
Modulus (lb/in2) 14–16×106 20–23×106 25–27×106
(GN/m2) 96–110 140–160 170–190
Charpy impact
Joules, 25°C nil 3–7 17
Fatigue limit
un-notched (ton/in2) 7–8 15–20 12–18
(N/mm2) 108–123 230–310 185–280
Machinability very good very good good
Corrosion moderate intermediate good
resistance
Ductile iron 89
Table 6.6 Specifications for compacted graphite iron: ASTM A842-85 (reapproved
1991) compacted graphite iron
Grade
250a 300 350 400 450b
Tensile strength (MPa) 250 300 350 400 450
Yield strength (MPa) 175 210 245 280 315
Elongation (%) 3.0 1.5 1.0 1.0 1.0
Hardness (HB) 179 max 143–207 163–229 197–225 207–269
aferritic grade
bpearlitic
Hardness not mandatory
Chapter 7
Malleable cast iron
Introduction
Malleable irons are cast white, that is, their as-cast structure consists of
metastable carbide in a pearlitic matrix. The castings must then be annealed
to convert the brittle carbide structure and develop a structure of roughly
spherical graphite aggregates in a matrix which can be either ferritic or
pearlitic, depending on composition and heat treatment.
There are two types of malleable iron, blackheart and whiteheart. Malleable
iron has a long history, whiteheart iron having been developed in 1722 bythe French metallurgist, Réaumur, while blackheart iron was developed in
the USA in 1820. Malleable iron was widely used for automotive and
agricultural components, pipe fittings, valves etc. but since the development
of spheroidal graphite ductile iron its use has declined, due to the high cost
of the annealing treatment which requires expensive furnace equipment.
Malleable iron is still widely used for small pipe fittings, electrical fittings
and builders hardware, particularly for thin section castings and castings
which are subsequently galvanised.
Whiteheart malleable
In the whiteheart process, the white, as-cast iron is decarburised during
annealing leaving a structure of iron carbide in a metallic matrix. When
fractured, the appearance is whitish, giving rise to the name, ‘whiteheart’.
Decarburisation is only possible in thin sections; in heavier sections, some
conversion of carbide to graphite nodules occurs so that the annealed casting
has a white rim with a core having different structure and mechanical
properties. This limits the applications to which it can be put. Whiteheart
can be melted in a cupola and is a low cost material which still finds
applications in small, thin section castings.
Composition of whiteheart malleable
Typical compositions are
Malleable cast iron 91
Before annealing After annealing
Total carbon 3.0–3.7% 0.5–2.0%
Silicon 0.4–0.8 0.4–0.7
Manganese 0.1–0.4 0.1–0.4
Sulphur 0.3 max 0.3 max
Phosphorus 0.1 max 0.1 max
Annealing is a combined decarburisation and graphitisation process
performed in an oxidising atmosphere. Originally it was done by packing
castings into iron ore mixtures but now it is carried out in continuous,
atmosphere controlled furnaces at about 1070°C. Small castings may be
fully decarburised and are referred to as weldable malleable irons. Table 7.1
lists the European specifications for whiteheart malleable iron. The USA has
no equivalent standard.
Table 7.1 Specifications for whiteheart malleable cast irons
Grade Test bar Tensile Elongation 0.2% Proof HB
dia. strength strength typical
(mm) (min) (%) (min)
(N/mm2) (N/mm2)
EN-GJMW-300-4 12 350 4 – 230
EN-GJMW-360-12 12 360 12 190 200
EN-GJMW-400-5 12 400 5 220 220
EN-GJMW-450-7 12 450 7 260 260
EN-GJMW-550-4 12 550 4 340 340
International ISO 5922–1981
Whiteheart
W 35-04 9 340 5 –
12 350 4 – 230 max
15 360 3 –
W 38-12 9 320 15 170
12 380 12 200 200 max
15 400 8 210
W 40-05 9 360 8 200
12 400 5 220 220 max
15 420 4 230
W 45-07 9 400 10 230
12 450 7 260 150 max
15 480 4 280
The European Standard CEN 1562:1997 has superseded the former national standards,
for example:
France: NF A32-701(1982); Germany: DIN 1692 (1982); UK: BS6681:1986.
Notes: It is advisable to consult the original standards for details of the mandatory
values, methods of testing etc.
USA has no standard for whiteheart malleable iron.
92 Foseco Ferrous Foundryman’s Handbook
Blackheart malleable iron
The iron is typically melted in a cupola and duplexed into an electric furnace
where temperature and composition are adjusted. The cupola metal has the
composition:
C Si Mn S P
2.5–2.6 1.1 0.2–0.3 0.2 0.1
The final composition in the electric furnace is:
C Si Mn S P Cr
 2.4–2.6 1.3–1.45 0.4–0.55 0.2 max 0.1 max 0.05 max
Castings are poured at around 1450°C. Sometimes small additions (around
0.01%) of bismuth are added in the ladle to ensure fully white as-cast
structures. White irons contract on solidification so to ensure freedom from
shrinkage, the castings must be fed, see Chapter 19. As-cast malleable iron
is extremely brittle, allowing feeders and running systems to be broken
easily from the castings. Castings which have abrupt changes of section
develop internal stresses on cooling which may be enough to cause cracking
of the castings after shakeout. Slow cooling in the mould may be needed to
avoid this happening.
The castings are annealed to develop the required graphite clusters (Fig.
2.3). A typical cycle is about 48 hours long (Fig. 7.1) it may be carried out in
batch-type or continuous furnaces in a controlled atmosphere to avoid
oxidation of the castings. The rate of cooling in the final section of the heat
1st stage 2nd stage
Te
m
pe
ra
tu
re
 (
°C
)
960
790
720
500
12 24 36 48 60
 Time (h)
Figure 7.1 Typical heat treatment cycle for a short cycle blackheart malleable iron.
(From Elliott, R. (1988) Cast Iron Technology, Butterworth-Heinemann, reproduced
by permission of the publisher.)
Malleable cast iron 93
treatment determines the matrix structure of the castings which can be
ferritic or pearlitic according to the physical properties required.
Specifications for malleable cast irons
Table 7.2 lists the European and International specifications for blackheart
malleable cast irons. The European Standard CEN 1562:1997 has superseded
the former national standards. Table 7.3 lists the US ASTM specifications.
Table 7.2 European and international specifications for blackheart malleable cast
irons
Grade Test bar Tensile Elongation 0.2% Proof HB
dia. (mm) strength (min.) (%) stress (min.) typical
(N/mm2) (N/mm2)
EN-GJMB-300-6 12 or 15 300 6 – 150 max
EN-GJMB-350-10 12 or 15 350 10 200 150 max
EN-GJMB-450-6 12 or 15 450 6 270 150–200
EN-GJMB-500-5 12 or 15 500 5 300 165–215
EN-GJMB-550-4 12 or 15 550 4 340 180–230
EN-GJMB-600-3 12 or 15 600 3 390 195–245
EN-GJMB-650-2 12 or 15 650 2 430 210–260
EN-GJMB-700-2 12 or 15 700 2 530 240–290
EN-GJMB-800-1 12 or 15 800 1 600 270–320
International Standard ISO 5922-1981
Blackheart
B30-06 12 or 15 300 6
B32-12 12 or 15 320 12 190 150 max
B35-10 12 or 15 350 10 200
Pearlitic
P45-06 12 or 15 450 6 270 150–200
P50-05 12 or 15 500 5 300 160–220
P55-04 12 or 15 550 4 340 180–230
P60-03 12 or 15 600 3 390 200–250
P65-02 12 or 15 650 2 430 210–260
P70-02 12 or 15 700 2 530 240–290
P80-01 12 or 15 800 1 600 270–310
The European Standard CEN 1562:1997 has superseded the former national standards,
for example:
France: NF A32-702(1982); Germany: DIN 1692 (1982); UK: BS6681:1986.
Notes: It is advisable to consult the original standards for details of the mandatory
values, methods of testing etc.
94 Foseco Ferrous Foundryman’s Handbook
Table 7.3 US specifications for blackheart malleable irons
Specification Grade Test bar Tensile Elong. Yield stress Hardness
diameter strength (%) (N/mm2) (HB)
(mm) (N/mm2)
ASTM A 47-90 220M10 15.9 340 10 220 156 max
Ferritic 32510 50000 psi 32000 psi
ASTM A220-88 280M10 15.9 400 10 280 149–197
Pearlitic 40010 60000 psi 40000 psi
310M8 15.9 450 8 310 156–197
45008 65000 psi 45000
310M6 15.9 450 6 310 156–207
45006 65000 psi 45000
340M5 15.9 480 5 340 179–229
50005 70000 psi 50000 psi
410M4 15.9 550 4 410 197–241
60004 80000 psi 60000 psi
480M3 15.9 590 3 480 217–269
70003 85000 70000 psi
550M2 15.9 650 2 550 241–285
80002 95000 psi 80000 psi
620M1 15.9 720 1 620 269–321
90001 105000 psi 90000 psi
ASTM A602-94 M3210 (10) (32000 psi) 156 max1
Automotive M4504 (4) (45000 psi) 163–2172
malleable M5003 (3) (50000 psi) 187–2412
castings M5503 (3) (55000 psi) 187–2413
M7002 (2) (70000 psi) 229–2693
M8501 (1) (85000 psi) 269–3023
ASTM A47-90 (reapproved 1995) covers ferritic malleable irons, a metric version
was reapproved in 1996.
ASTM A220-88 (reapproved 1993 including a metric version) covers pearlitic malleable
irons.
ASTM A602-94 covers automotive malleable castings.
Note: ASTM A602-94 specifies only hardness and heat treatment. Annealed1 Air-
quenched2 and tempered3 Liquid quenched and tempered.
Chapter 8
Special purpose cast irons
Heat resisting alloys
Unalloyed cast iron shows only slight scaling and no growth at temperatures
up to 350°C for times of up to 10 years. At 450°C scaling and growth will
occur in less than one year in most grey, ductile and malleable cast irons. To
achieve greater resistance to heat, special purpose irons must be used.
Temperatures up to 600°C
Unalloyed grey irons can be used up to about 600°C. The presence of
phosphorus up to 1.0% improvesthe scaling resistance and can be used in
applications such as fire bars where mechanical strength is not a major
consideration.
Temperatures up to 700°C
The addition of about 0.5% Cr improves the oxidation resistance of grey
irons and is also used for fire bars. Automotive exhaust manifolds and
turbo-charger casings are subjected to increasingly high temperatures in
modern engines, unalloyed cast iron can be used at temperatures up to
about 600°C, but for higher temperature service it is necessary to alloy the
iron with Cr and Mo, e.g.
Low alloy grey iron
C Si Mn S P Cr Mo
3.0–3.4 1.6–2.8 0.4–1.0 <0.12 0.1–0.4 0.5–2.0 0.3–0.5
Temperatures up to 750°C
Ductile (spheroidal graphite) irons with silicon in the range 4–6% have
good resistance to scaling and growth and good dimensional stability up to
about 750°C. Molybdenum up to 0.5% may be added to improve the high
96 Foseco Ferrous Foundryman’s Handbook
temperature creep resistance. They are used for exhaust manifolds and turbo-
charger casings and are better able to resist thermal stress than grey iron
castings. Typical compositions are:
High silicon ductile iron
C Si Mn P Mo
3.2 4.0 0.3 max 0.05 max 0.5
2.9 4.0 0.3 max 0.05 max 0.5
2.6 6.0 0.3 max 0.05 max 0.5
Temperatures up to 850°C
For heat resistance up to 850°C, nickel alloy cast irons, known as Ni-resist (a
trade name of the International Nickel Company) are used. Nickel in
combination with Mn and Cu produces a stable austenitic matrix and Cr in
combination with Ni forms an effective oxidation resistant scale. Most
countries have similar standard specifications for austenitic cast irons, based
on the original Ni-Resist specifications. Each country designates the alloys
differently. Table 8.1 lists the designations of the flake graphite austenitic
irons. Table 8.2 lists the specifications of austenitic flake graphite irons.
Spheroidal graphite Ni-resist can also be made. Table 8.3 lists the
international designations. Table 8.4 lists the British specifications.
Temperatures up to 1000°C
High Cr white irons have excellent resistance to oxidation at temperatures
up to 1000°C and can be used in applications where they are not subjected
to impact loading. They are used for furnace parts, sinter pallets, recuperator
tubes etc. Typical analyses are:
C Si Mn S P Cr
2.0 1.4 1.0 0.1 0.1 max 14.0
2.8 1.8 1.6 17.0
1.0 1.0 0.7 30.0
1.3 1.3 1.0 33.0
Ingot moulds
Products such as ingot moulds, slag ladles, pig-moulds etc. are subjected in
use to severe thermal cycling which induces distortion and crazing. High
carbon iron is used for such applications, typically: (Continued on p. 101)
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ar
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in
te
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as
 a
 g
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Special purpose cast irons 101
C Si Mn S P
3.6–3.9 1.4–1.8 0.7–1.0 as low as possible
The iron is of eutectic composition or slightly hyper-eutectic, since this is
found to give the maximum mould life. Compacted graphite iron is also
used for this application (see p. 84).
Corrosion resistant cast irons
Unalloyed cast irons exhibit reasonable corrosion resistance, particularly to
alkali environments, but special alloys have been developed for use in
corrosive conditions. These include, high nickel (Ni-Resist), high silicon
and high chromium alloys. Table 8.5 summarises the corrosion resistance of
various alloy irons in different media.
Table 8.5 Corrosion resistance of cast irons
Unalloyed grey, Ni-Resist High silicon High chromium
ductile and See Table 8.1 10–16% Si 30% Cr, 1–2% C
malleable
Atmospheric B A A A
including coastal
Water soft B A A A
hard A A A A
sea C A A A
Dilute acid C B A A1
Concentrated acid C2 C A3 C
Dilute alkali A A C A
Concentrated alkali B A C C
Notes: A – Good resistance 1 Unalloyed iron resists concentrated sulphuric
acid quite well
B – Medium resistance 2 High silicon irons do not resist hydrofluoric
acid
C – Poor resistance 3 High chromium irons are less resistant to
hydrochloric acid
Ni-Resist alloy irons are used for the manufacture of pumps for the handling
of sulphuric acid and alkalis, for sea water pumps and for handling sour
crude oils in the petroleum industry.
High silicon cast irons, 10–16% Si, are suitable for use in chemical plant
and for cathodic protection anodes. The grades shown in Table 8.6 are used.
High silicon irons are low strength, brittle materials which are susceptible
to cracking due to stresses induced by cooling. Moulds and cores used for
their manufacture should have good breakdown properties. Electric furnace
melting is necessary because of their low carbon content. The alloys are
102 Foseco Ferrous Foundryman’s Handbook
prone to unsoundness due to hydrogen gas and care must be taken during
melting to avoid contact with hydrogen, by the avoidance of moisture on
charge materials and refractories and maintaining low levels of Al in the iron.
Heat treatment is advisable to eliminate internal stresses, the castings
should be stripped from the moulds as hot as possible and charged into a
furnace at about 600°C then heated to 750–850°C for 2–8 hours, depending
on metal section. They should then be slowly cooled to below 300°C before
removing from the furnace.
High silicon irons have high hardness and are difficult to machine; grinding
is preferred.
Wear resistant cast irons
Wear resistant alloy irons are an important class of cast irons, they find wide
application for the manufacture of mineral crushing plant, e.g hammers for
rock crushers, grinding balls, liners for crushing mills etc. They are also
used in shot blasting machines for impellers, liners etc. Three types of cast
iron are used:
Unalloyed and low alloy grades of white iron having a structure of massive
carbides in a pearlitic matrix. These alloys are extremely brittle and have
been largely superseded by tougher, alloyed white irons.
Ni-hard irons containing Ni to increase hardenability by ensuring that
austenite transforms to martensite after heat treatment. They also contain
Cr to increase the hardness of the carbide.
High Cr-Mo white irons combining abrasion resistance with toughness.
The Mo increases hardenability allowing heavy section castings to be
made with a martensitic structure, either as cast or heat treated.
Low alloy cast irons
These include irons having the compositions:
Table 8.6 High silicon cast irons
Grade C (max) Si Mn (max) S (max) P (max) Cr
Si 10 1.2 10.00–12.00 0.5 0.1 0.25 –
Si 14 1.0 14.25–15.25 0.5 0.1 0.25 –
SiCr 14 4 1.4 14.25–15.25 0.5 0.1 0.25 4.0–5.0
Si 16 0.8 16.00–18.00 0.5 0.1 0.25 –
Grade Si 14 is used for general applications
Si 10 has higher tensile strength but lower corrosion resistance
Si 16 has high corrosion resistance but lower strength
Si Cr 14 4 is used for the manufacture of cathodic protection anodes
For further details, refer to BS 1591.
Special purpose cast irons 103
BS 4844:1986 C Si Mn Cr
1A,1B,1C 2.4–3.4 0.5–1.5 0.2–0.8 2.0 max
Grade Hardness (min) HB
Thickness < 50 mm Thickness > 50 mm
1A 400 350
1B 400 350
1C 250 200
Such irons are extremely brittle and have been largely superseded by alloyed
irons.
Ni-hard irons
The first alloyed irons to be developed were the Ni-hards (a trade name of
the International Nickel Company). They contain Ni to increase hardenability,
ensuring that austenite transforms to martensite after heat treatment. The
Cr content increases the hardness of the eutectic carbide. The choice of alloy
composition depends on casting thickness and intended use. For maximum
abrasion resistance, the C content should be at the top of the range, 3.2–
3.6%, but for impact resistance it is usual to use lower carbon contents, 2.7–
3.2%. Table 8.7 lists a number of national specifications for alloy irons of the
Ni-hard type. Note that the correspondence between specifications is not
exact and the standards themselves must be referred to for details.
Ni-hards are usually stress relieved at 200–230°C for at least 4 hours to
improve strength and impact resistance.
High Cr-Mo irons
The addition of Cr in the range 12–28%, together with Ni and Mo forms a
range of alloys which combines abrasion resistance with toughness suitable
for large size equipment in the mining, coal and mineral processing industries.
Eutectic carbides of the form, M7C3 are formed and the matrix can be austenitic,
martensitic or pearlitic according to the application. Some components may
be cast pearlitic to aid machining, then heat-treated to give an abrasion
resistant martensitic structure. Tables 8.8 and 8.9 list specifications of this
type.
Production of high chromium irons
An induction furnace is normally used to achieve the required temperature.
Ta
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 1
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Special purpose cast irons 107
The Cr–Fe oxides formed during melting attack silica lining materials, so
alumina linings should be used. Charges are based on steel scrap and foundry
returns with additions of high and low carbon ferrochromium to obtain
iron of the required carbon content. Ferromolybdenum is added as needed.
A loss of about 5% of the Cr content will occur during melting.
A melting temperature of 1600–1650°C is needed for the low carbon, high
Cr irons, but a lower temperature of 1550–1600°C is sufficient for the higher
carbon alloys.
A viscous oxide film forms on the surface of the molten metal in the
furnace and the ladle. The iron must be carefully skimmed before pouring,
and running systems must be designed to trap oxide dross. Metal filters
should be used if possible. To avoid oxide defects on the casting surface,
gating should provide rapid filling of the mould with minimum turbulence.
Chapter 9
Types of steel castings
Introduction
Steel is the most versatile of the structural engineering materials, so that
more grades of steel are available for casting than any other alloy type. The
casting of steel presents a number of special problems due mainly to the
high casting temperature, typically 1550–1600°C, and the volume shrinkage
(6.0–10.0%) that occurs on freezing. Steel castings range in size from a few
grams to hundreds of tonnes. Steel castings are often used in critical situations
where optimum mechanical properties are essential so that freedom from
casting defects is particularly important. The advantages of cast steel over
other cast metals, such as ductile iron, are:
High modulus – minimising deflection under heavy static loading
Shock and impact resistance – to cope with severe dynamic loading
Heat-treatable – to give the required toughness, hardness and strength
Weldable – so that castings can be joined to wrought steel products
High temperature strength – special alloys are available
Steel castings compete in many areas with steel weldments. In welding, it is
difficult to avoid stress concentrations at junctions while castings have well-
radiused joints so that fatigue resistance of cast steel junctions is superior to
that of welded junctions. Also welds, especially in large structures, are not
always amenable to stress-relieving after welding so that internal stresses
are likely to be greater in weldments than in steel castings. This may lead to
distortion of weldments or even failure in highly stressed components.
Castings allow freedom of design which is not possible with weldments.
The main applications of steel castings, roughly in order of tonnage used
in the UK, are:
Valves, pumps and compressors
Construction and earth moving equipment
Crushing, grinding, quarrying and dredging
Oil and gas rigs
Mining equipment
Motor vehicles
Defence equipment
Railways
Types of steel castings 109
Shipbuilding
Iron and steelworks
Nuclear power plant
General engineering equipment
Electrical plant
Agricultural equipment
While the overall tonnage of steel castings has been on a downward trend
for a number of years, the overall value has increased due to a growing
trend towards increased quality standards, reflecting the high standards
needed for nuclear plant, gas and oil rigs etc.
Processes used for steel castings are:
Green sand for high volume castings
Chemically bonded sand where numbers required are smaller
Ceramic block moulds for castings requiring particularly good
surface finish
Lost wax investment casting for smaller castings made in large
numbers where good surface finish and
dimensional accuracy is needed
The Lost Foam process is not normally used for steel casting because of the
danger of carbon pick-up from the foam pattern.
Specifications for steel castings
Steel casting specifications in Europe are undergoing major changesas new
European specifications are being drawn up. At the time of writing, the
only European standard to be issued in the UK is BS EN 10213:1996 covering
Steel Castings for Pressure Purposes. During the next few years, EN standards
covering steels for General Engineering, Corrosion Resisting, Heat Resisting,
Wear Resisting, Structural and Centrifugal applications will replace the
existing national standards in European countries.
Until the new standards are issued, individual national standards apply.
However, attention should be paid to the International Standard ISO 4990-
1986 Steel Castings, General Technical Delivery Requirements which specifies
the methods of testing steel castings and other matters which need to be
agreed between purchaser and supplier. The contents of this standard are
being incorporated into the forthcoming European standard.
ISO 4990 requires the purchaser to supply details with the enquiry covering:
A description of the casting(s) by pattern number or drawing
Dimensional tolerances, machining allowances and datum points for
machining
The material standard and grade of steel
110 Foseco Ferrous Foundryman’s Handbook
The type of document required for inspection and testing
Additional information such as agreed manufacturing method
Size of test lot
Procedures for marking, machining, protection, packaging, loading,
dispatching and the destination
Submission of sample castings
Methods of statistical control
Inspection procedures
The standard lists details of inspection and testing to be carried out by the
manufacturer including:
Documents required
Sampling, preparation of test pieces and mechanical and chemical test
methods
Test blocks
Heat treatment
Repair welding
Non-destructive tests
Special tests such as intergranular corrosion and pressure tests
Test reports must provide the required traceability of the castings they
represent
It is normally required that the manufacturer shall maintain records of results
of all the chemical and mechanical tests performed by the foundry for a
minimum of 5 years.
Other ISO Standards detail testing methods:
ISO 148 Steel – Charpy impact test (V-notch).
ISO/R 783 Mechanical testing of steel at elevated temperatures –
Determination of lower yield stress and proof stress and proving
test.
ISO 2605/1 Steel products for pressure purposes – Derivation and veri-
fication of elevated temperature properties – Part 1: Yield or
proof stress of carbon and low alloy steel products.
ISO 2605/2 Steel products for pressure purposes – Derivation and veri-
fication of elevated temperature properties – Part 2: Proof stress
of austenitic steel products.
ISO 3452 Non-destructive testing – Penetrant inspection – General
principles.
ISO 3651/2 Austenitic stainless steels – Determination of resistance to
intergranular corrosion – Part 2: Corrosion test in a sulphuric
acid/copper sulphate medium in the presence of copper
turnings (Monypenny Strauss test).
ISO 5579 Nondestructive testing – Radiographic examination of metallic
materials by X- and gamma rays – Basic rules.
ISO 6506 Metallic materials – Hardness test – Brinell test
Types of steel castings 111
ISO 6892 Metallic materials – Tensile testing.
ISO 8062 Castings – System of dimensional tolerances.
British Standards for steel castings
A number of British Standard Specifications cover steel castings. There are
equivalent standards in all industrialised countries, but the number of
specifications is so great that it is not possible to list them here. The British
Standards for steel castings include:
BS 1504 Steel Castings for Pressure Purposes
BS 1965 Pt 2 Butt Welding Pipe Fittings for Pressure Purposes (Austenitic
Stainless Steel)
BS 3100 Steel Castings for General Engineering Purposes
Section 2: Carbon and Carbon–Manganese Steels
Section 3: Low Alloy Steel Castings
Section 4: Corrosion Resisting, Heat Resisting and
High Alloy Steel Castings
BS 3146 Part 1 Investment Castings in Metal
Carbon and Low Alloy Steels
Corrosion and Heat Resisting Steels, Nickel and Cobalt
Base Alloys
Vacuum Melted Alloys
BS 2772 Iron and Steel for Colliery Haulage and Winding Equipment
1.5% Mn Steel Castings for Mine Car Couplers
BS 4473 Railway Rolling Stock Material
Cast Wheel Centres in Unalloyed Steel for Tyred
Wheels
BS 4534 Weldable Cr-Ni Centrifugally Cast Steel Tubes
BS Aerospace Series Specifications
Lists of equivalent standards are given in British and Foreign Specifications for
Steel Castings, published by the Castings Development Centre (formerly the
Steel Castings Research and Trade Association) East Bank Road, Sheffield
S2 3PT, 4th Ed. 1980. The large number of specifications may be judged
from the fact that the above book lists over 180 British specifications alone.
Types of steel castings
It is convenient to classify steels into three groups
Carbon steels
Low and medium alloy steels
High alloy steels
112 Foseco Ferrous Foundryman’s Handbook
Carbon steels
These are steels in which carbon is the main alloying element, other elements
such as manganese and silicon are present for the purposes of deoxidation.
The effectiveness of heat treatment in increasing the strength of the steel
depends on carbon content and carbon steels may be further subdivided
into
Low carbon steel <0.20%C
Medium carbon steel 0.20–0.50%C
High carbon steel >0.50%C
Applications of carbon steel castings include
Ship’s structural castings
Railway rolling stock
Automotive castings
Hot metal ladles
Rolling mill equipment
Rolls and rollers
Machines and tools
Mine and quarry equipment
Oil and petroleum equipment
Typical medium carbon steel specifications are shown in Table 9.1 (from BS
3100). There are equivalent specifications in other countries, for example:
UK BS 3100 A1 A2 A3
USA ASTM A27-77 N-1 A27-77 N-2 A148-73 gr. 80-40
Germany DIN 1681 GS-45 GS-52 GS-60
Carbon steels are most frequently used in the annealed, normalised or
annealed and normalised conditions, though other heat treatments may be
used to develop special properties, for example, for magnetic permeability.
Low alloy and medium alloy steels
Castings in this class normally contain amounts of manganese or silicon
greater than is needed for deoxidation (e.g. >1% Mn) or to which other
elements have been specially added. Alloy steels will contain Ni, Cr or Mo
as main alloying constituents and smaller amounts of V, Cu and possibly B.
These elements are added primarily to alter hardenability so that the required
properties can be obtained in different section thicknesses.
Pearlitic manganese steels (1.5%Mn), Table 9.1, are used where strengths
a little higher than attainable in plain carbon steels together with good
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 0
.0
4%
M
n 
w
ill
 b
e 
p
er
m
it
te
d
 u
p
 t
o 
a 
m
ax
. o
f 
1.
10
.
(2
) 
R
es
id
u
al
 e
le
m
en
ts
: t
he
 t
ot
al
 s
ha
ll 
no
t 
ex
ce
ed
 0
.8
0%
.
(3
) 
E
it
he
r 
a 
be
nd
 t
es
t 
or
 a
n 
im
p
ac
t 
te
st
 m
ay
 b
e 
sp
ec
if
ie
d
.
(4
) 
Im
p
ac
t 
te
st
 m
an
d
at
or
y 
on
ly
 i
f 
sp
ec
if
ie
d
 b
y 
p
u
rc
ha
se
r.
(5
) 
L
im
it
in
g 
se
ct
io
n 
th
ic
kn
es
s,
 1
00
 m
m
.
(6
) 
L
im
it
in
g 
se
ct
io
n 
th
ic
kn
es
s,
 5
3 
m
m
.
T
hi
s 
ta
bl
e 
is
 i
nt
en
d
ed
 o
nl
y 
as
 a
 g
u
id
e,
 r
ef
er
 t
o 
th
e 
B
ri
ti
sh
 S
ta
nd
ar
d
 f
or
 d
et
ai
ls
.
114 Foseco Ferrous Foundryman’s Handbook
toughness are required. Applications are excavating buckets, travelling wheels,
gears, tractor track links and pneumatic tool parts.
Frequently used alloy steels are 11/2% Mn-Mo, 11/4% Cr-Mo, 0.75% Ni-
Cr-Mo, 11/2% Ni-Cr-Mo and 3% Cr-Mo (Table 9.2). Such higher strength
steels find use for gears, shaft pinions, impellers, rolls, rollers, crusher heads,
mill liners, crankshafts, cement processing machinery, fittings and components
in the oil industry.
Steel castings with a hard skin and a very tough core may be obtained by
local hardening (flame or induction hardening or carburising or nitriding).
Austenitic manganese steel
This widely used steel contains from 10–14%Mn and 1.0–1.4%C (typically
12%Mn, 1.25%C) (Table 9.3). The as-cast structure contains carbides and
other transformation products which produce brittleness. The castings are
therefore austenitised at 1000°C or above and quenched in water, producing
a fully austenitic structure that is quite tough. On account of their unique
ability to resist pounding and severe abrasive wear, Mn-steel castings are
used for railway trackwork, dredging, excavating, pulverising and crushing
equipment for mines and quarries, cement mills etc.
High alloy steels
These are used where corrosion resistance or heat resistance is required.
The alloys may be subdivided into three main groups:
Fe-Cr
Fe-Cr-Ni
Fe-Ni-Cr
The iron-chromium steels contain little or no nickel and 10–30%Cr. The Cr
content influences their resistance to scaling, the 13%Cr steels having
reasonable oxidation resistance up to 650°C while 28%Cr steel can be used
up to around 1100°C. The 13%Cr steels are used for pumps and steam
turbine equipment. 20–30%Cr steels are used in the chemical industry for
pump parts and valves, also for furnace parts, grates, kiln parts etc.
The iron-chromium-nickel alloys include the well-known 18/8 stainless
steels to which additions of Nb or Ti may be used to stabilise the austenite
on heating. Mo may also be added and Ni raised to 10% to allow the steel
to be used at higher temperatures (up to 1100°C) and improve the corrosion
resistance. High corrosion resistance and toughness require the lowest carbon
possible and special melting techniques allow figures as low as 0.03%C to
be achieved, although achieving such low carbon contents at the surface of
the casting is not easy since most moulding materials can cause surface
Ta
bl
e 
9.
2
B
S 
31
00
:1
97
6 
St
ee
l 
C
as
ti
ng
s 
fo
r 
G
en
er
al
 E
ng
in
ee
ri
ng
 P
u
rp
os
es
L
ow
 A
llo
y 
St
ee
l 
C
as
ti
ng
s
C
–1
/
2 
M
o
11
/
4C
r–
M
o
21
/
4 
C
r–
M
o
3%
C
r–
M
o
11
/
4%
C
r–
 M
o
B
1
B
2
B
3
B
4
B
W
4
C
he
m
ic
al
 c
om
po
si
ti
on
 (
%
)
m
in
m
ax
m
in
m
ax
m
in
m
ax
m
in
m
ax
m
in
m
ax
C
–
0.
20
–
0.
20
–
0.
18
–
0.
25
0.
55
0.
65
Si
0.
20
0.
60
–
0.
60
–
0.
60
–
0.
75
–
0.
75
M
n
0.
50
1.
00
0.
50
0.
80
0.
40
0.
70
0.
30
0.
70
0.
50
1.
00
P
–
0.
05
–
0.
05
–
0.
05
–
0.
04
–
0.
06
S
–
0.
05
–
0.
05
–
0.
05
–
0.
04
–
0.
06
C
r
–
0.
25
1.
00
1.
50
2.
00
2.
75
2.
50
3.
50
0.
80
1.
50
M
o
0.
45
0.
65
0.
45
0.
65
0.
90
1.
20
0.
35
0.
60
0.
20
0.
40
N
i
–
0.
40
–
0.
40
–
0.
40
–
0.
40
–
–
C
u
–
0.
30
–
0.
30
–
0.
30
–
0.
30
–
–
M
ec
ha
ni
ca
l 
p
ro
p
er
ti
es
T
S 
(N
/
m
m
2 )
46
0
–
48
0
–
54
0
–
62
0
–
–
–
0.
2%
P
S 
(N
/
m
m
2 )
26
0
–
28
0
–
32
5
–
37
0
–
–
–
E
lo
ng
at
io
n 
(%
)
18
–
17
–
17
–
13
–
–
–
A
ng
le
 o
f 
be
nd
12
0
–
12
0
–
12
0
–
12
0
–
–
–
R
ad
iu
s 
of
 b
en
d
 (
t)
1.
5t
–
1.
5t
–
3t
–
3t
–
–
–
C
ha
rp
y 
Im
p
ac
t 
(J
)
20
–
30
–
25
–
26
–
–
–
H
ar
d
ne
ss
 (
H
B
)
–
–
14
0
21
2
15
6
23
5
17
9
25
5
34
1
–
N
ot
es
:
t 
=
 t
hi
ck
ne
ss
 o
f 
th
e 
te
st
 p
ie
ce
T
hi
s 
ta
bl
e 
is
 i
nt
en
d
ed
 o
nl
y 
as
 a
 g
u
id
e,
 r
ef
er
 t
o 
th
e 
B
ri
ti
sh
 S
ta
nd
ar
d
 f
or
 d
et
ai
ls
.
116 Foseco Ferrous Foundryman’s Handbook
recarburisation due to the breakdown of carbon-containing binders. These
corrosion resistant steels are widely used for marine fittings, pump parts,
valve bodies, impellers etc.
One of the most widely used cast stainless steels is BS 3100: 316C16
(Table 9.4) an 18Cr/10Ni/2.5Mo cast equivalent of 316 wrought stainless
alloy (US equivalent, CF-8M).
Table 9.3 BS 3100:1976 Steel Castings for General Engineering
Purposes
Austenitic Manganese Steel Castings
BW10
Chemical composition (%) min max
C 1.00 1.25
Si – 1.00
Mn 11.00 –
P – 0.07
S – 0.06
Cr – –
Mo 0.45 –
Ni – –
Cu – –
The mechanical properties shall be agreed between the manufacturer
and the purchaser.
For special applications, max. carbon may be increased to 1.35%.
This table is intended only as a guide, refer to the British Standard
for details.
Table 9.4 Cast stainless steel BS3100: 316C16
C Si Mn P S Cr Mo Ni
0.08 1.5 2.0 0.04 0.04 17–21 2.0–3.0 10 min
Mechanical properties
UTS (N/mm2) 480
0.1%PS (N/mm2) 240
Elongation (%) 26
Impact (J) 34
(Refer to BS3100 for details)
Such steels can be used at temperatures up to about 550°C making them
suitable for high pressure steam valves for nuclear and chemical applications
as well as for valves and pumps for handling hot acids and also marine
fittings. Unlike the wrought alloys, cast stainless steels contain from 5–40%
ferrite which provides strength, improves weldability and maximises
resistance to corrosion in specific environments.
Alloys for heat resisting applications contain 25%Cr and 12%Ni for use
up to 1050°C and 25%Cr–20%Ni for use up to 1100°C. They are used for
exhaust manifolds, burner nozzles, furnace parts, stack flues etc.
Types of steel castings 117
The iron-nickel-chromium alloys are used for heat resisting applications.
Widely used alloys include one containing 17%Cr, 25%Ni, and one having
37%Ni, 15%Cr. The castings are used for furnace parts, salt and cyanide
pots, annealing trays etc.
Typical steel casting compositions of the above steel types are given in
Table 9.5.
Duplex steels
The severe conditions experienced in off-shore drilling platforms and other
marine applications require high strength corrosion resistant steels. Alloys
having a duplex ferrite-austenite microstructure have been developed for
this purpose (Table 9.6). High hardness is produced by the high copper
content (3%). The steel is heat treated by austenitising at around 1100°C
when the copper dissolves. Oil quenching retainsthe copper in solution,
subsequent ageing at around 480°C produces a ferrite-austenite structure
with precipitated copper increasing strength and hardness.
Only a few specifications are quoted here. Details of Steel Casting
Specifications world-wide are presented in British and Foreign Specifications
for Steel Castings, published by CDC, East Bank Road, Sheffield S2 3PT. The
large number of specifications may be judged from the fact that the above
book lists over 180 British specifications alone.
Further details of the properties of all the above steels may be obtained
from Steel Castings Design Properties and Applications, edited by W.J. Jackson,
published by CDC, East Bank Road, Sheffield S2 3PT.
The Steel Castings Handbook, sixth edition, by Steel Founders’ Society of
America and ASM International, 1995 contains full details of material selection,
mechanical properties, design and manufacture of castings etc.
Physical properties of steels
Table 9.7 gives typical physical properties of commonly used cast steels.
These figures should be regarded as approximate only, since the exact
composition and state of heat treatment affects the properties. Where
properties are quoted for a particular temperature, the figure is the average
value from room temperature to the quoted temperature.
Selection of suitable steel for casting
The choice and specification of a suitable steel for a specific application is
far from easy. Not only is it necessary to specify an alloy having suitable
properties: strength, hardness, fatigue properties, low temperature strength,
Ta
bl
e 
9.
5
B
S 
31
00
:1
97
6 
St
ee
l 
C
as
ti
ng
s 
fo
r 
G
en
er
al
 E
ng
in
ee
ri
ng
 P
u
rp
os
es
A
llo
y 
St
ee
l 
C
as
ti
ng
s
13
%
C
r
25
–3
0%
C
r
18
/1
0C
rN
i
25
/2
0C
rN
i
42
0C
29
45
2C
12
31
6C
16
31
0C
40
C
he
m
ic
al
 c
om
po
si
ti
on
 (
%
)
m
in
m
ax
m
in
m
ax
m
in
m
ax
m
in
m
ax
C
–
0.
20
1.
00
2.
00
–
0.
08
0.
30
0.
50
Si
–
1.
00
–
2.
00
–
1.
50
–
1.
50
M
n
–
1.
00
–
1.
00
–
2.
00
–
2.
00
P
–
0.
04
–
0.
06
–
0.
04
–
0.
04
S
–
0.
04
–
0.
06
–
0.
04
–
0.
04
C
r
11
.5
0
13
.5
0
25
.0
0
30
.0
0
17
.0
0
21
.0
0
24
.0
0
27
.0
0
M
o
–
–
–
1.
50
2.
00
3.
00
–
1.
50
N
i
–
1.
00
–
4.
00
10
.0
0
–
19
.0
0
22
.0
0
C
u
–
–
–
–
–
–
–
–
M
ec
ha
ni
ca
l 
P
ro
p
er
ti
es
T
S 
(N
/
m
m
2 )
69
0
–
48
0
–
48
0
–
62
0
–
0.
2%
P
S 
(N
/
m
m
2 )
46
5
–
28
0
–
24
0
–
37
0
–
E
lo
ng
at
io
n 
(%
)
11
–
17
–
26
–
13
–
A
ng
le
 o
f 
be
nd
–
–
12
0
–
–
–
12
0
–
R
ad
iu
s 
of
 b
en
d
 (
t)
–
–
1.
5t
–
–
–
3t
–
C
ha
rp
y 
Im
p
ac
t 
(J
)
–
–
30
–
34
–
26
–
H
ar
d
ne
ss
 (
H
B
)
20
1
25
5
14
0
21
2
–
–
17
9
25
5
T
hi
s 
ta
bl
e 
is
 i
nt
en
d
ed
 o
nl
y 
as
 a
 g
u
id
e,
 r
ef
er
 t
o 
th
e 
N
at
io
na
l 
St
an
d
ar
d
s 
fo
r 
d
et
ai
ls
.
Types of steel castings 119
Table 9.6 Duplex steel GX2CrNiMoCN25-6-3-3
C Si Mn P S Cr Mo Ni Cu N
0.03 1.0 1.50 0.035 0.025 24.5– 2.5– 5.0– 2.75– 0.12–
26.5 3.5 7.0 3.5 0.22
Mechanical properties:
UTS (N/mm2) 650–850
0.1%PS (N/mm2) 480
Elongation (%) 22
Impact (J) 50
Table 9.7 Physical properties of some steels
Composition Temp.°C Density Specific Thermal Thermal Electrical
(g/cm3) heat expansion conductivity resistivity
capacity coeff. (W/m.K) (micro-
(J/kg.K) (10–6/K) ohms.m2/m)
Carbon steels RT 7.86 59.5 13.2
100 482 12.19 57.8 19.0
200 523 12.99 53.2 26.3
400 595 13.91 45.6 45.8
600 741 14.68 36.8 73.4
800 960 14.79 28.5 108.1
1000 13.49 27.6 116.5
Low alloy RT 7.85 25.4
steels 100 456 12.45 48.2 30.6
200 477 13.2 45.6 39.1
400 532 14.15 39.4 60.0
600 599 14.8 33.9 88.5
Stainless RT 7.92 15.9 69.4
18/8 100 511 14.82 16.3 77.6
200 532 16.47 17.2 85.0
400 569 17.61 20.1 97.6
600 649 18.43 23.9 107.2
800 641 19.03 26.8 114.1
1000 28.1 119.6
13%Cr 100 7.75 482 11.0 24.3 57.0
wear resistance, corrosion resistance, high temperature strength and resistance
to oxidation etc. but it is usually necessary to define the inspection procedures
to be used. These will include
Visual examination of the casting surface to determine surface roughness
and freedom from cracks
Magnetic particle surface examination
Liquid penetrant surface examination
Radiographic inspection, usually in comparison to a system of reference
radiographs
120 Foseco Ferrous Foundryman’s Handbook
Ultrasonic testing, where heavy sections prohibit the use of radiography
Pressure or leak testing
Dimensional inspection
Statistical process control
Quality Assurance usually in accordance with a standard such as ISO
9002 or ISO 4990 Steel Castings – General Technical Delivery Requirements
The cost of minimum specification requirements is included in the basic
casting price, but additional testing will involve additional costs which
must be agreed between customer and supplier before castings are ordered.
Chapter 10
Melting and treatment of
steel for casting
Large steel foundries may use electric arc furnaces but induction furnaces
are the most commonly used melting furnaces for making steel castings.
Arc furnaces are capable of using low cost scrap charges, since refining
takes place in the furnace but arc furnaces have limitations since there is
always some pick-up of carbon from the graphite electrodes, so that very
low carbon stainless steels (<0.03%C) cannot be made. Refining is not possible
in the induction furnace, so a carefully selected charge must be used, but
any type of steel may be melted.
Arc furnace melting
The furnace consists of a refractory-lined mild steel shell, circular in section
and having a dished bottom. The refractory roof, usually water-cooled, has
three graphite electrodes projecting through it into the charge. The electrodes
can be raised and the roof lifted hydraulically and swung aside to allow the
furnace to be charged by a drop bottom charge bucket. The furnace is tilted
forward for tapping and backward for slag removal (Fig. 10.1).
Electrode arms above the roof supply three-phase power to the electrodes
and allow each electrode to be independently raised or lowered mechanically.
The length of the arc governs the power input to the furnace, regulators
measure the current in each electrode and control it automatically by
continuously adjusting the position of the electrode to maintain an optimum
arc length.
500–600 kWh of electricity is required to melt and raise to casting
temperature 1 tonne of steel. Furnaces are usually rated at 500 kVA per
tonne to give a melting time of about 11/2 hours.
The electrodes are made of graphite and are consumed during operation
through oxidation, volatilisation and breakage so they must be replaced as
necessary. A 3 tonne furnace typically uses electrodes of 200 mm diameter.
Electrode consumption is a significant factor in the cost of arc melting and
figures vary from 3–10 kg/tonne of steel melted depending on the type of
steel being produced and the practice used.
122 Foseco Ferrous Foundryman’s Handbook
Refractories
Arc furnace refractories can be ‘acid’, ‘basic’ or ‘neutral’ depending on the
melting practice used. Basic linings of dolomite or magnesite are the most
commonly used in steel foundries. A safety lining of firebrick is installed in
the steel shell of the furnace, followed by an inner lining of magnesite or
dolomite bricks. The working hearth is then formed by ramming tarred
dolomite or magnesite. Side walls are built up from tarred dolomite or steel-
clad magnesite bricks. The lining is then dried and fired. Roofs are expected to
have a long, maintenance-free life and may be made of high alumina refractory.
Melting practice in the basic lined arc furnace
The use of basic slags, oxidising or reducing in nature, allows phosphorus
and sulphur to be reduced to low levels so that the basic lined furnace is
very versatile, allowing good quality steel to be made from poor quality scrap.
Melting in a basic arc furnace can be a oneor two stage process using first
an oxidising slag then, if necessary, a reducing one. The charge, usually of
foundry returns and purchased steel scrap, is made up in a drop-bottom
charging bucket adding limestone and sometimes iron ore to the charge to
make the first oxidising slag which will remove phosphorus. Prior to the
Figure 10.1 Schematic diagram of an arc furnace showing typical refractories
used in acid and basic practices. (From Jackson, W.J. and Hubbard, M.W., Steelmaking
for Steelfounders, 1979, SCRATA. Courtesy CDC.)
Silica brick or
high alumina brick
Unburnt metal encased
magnesite-chrome brick
Magnesite brick
Tapping hole
sleeve
Fireclay brick
Magnesite brick
Grain magnesite
Basic furnace lining
Work
door
Top of
sill plate
Silica brick
Water cooled
arches & jambs
Silica brick
Fireclay brick
Ground silica ganister
Acid furnace lining
Melting and treatment of steel for casting 123
scrap being dropped into the furnace, some form of recarburiser such as
anthracite, coke or crushed electrodes is placed on the furnace bottom to
ensure sufficiently high carbon content at melt-out to give an adequate
‘boil’. When the charge is melted, the boil is induced by adding iron ore or
gaseous oxygen to the melt. The oxygen reacts with carbon in the melt
forming bubbles of carbon monoxide which rise through the metal giving
the appearance of boiling. The vigorous stirring action of the boil ensures
effective reaction of the metal with the slag and removes hydrogen and
nitrogen from the melt. The boil also removes carbon from the melt. The
carbon content of the melt is taken below the required finishing carbon and
the boil stopped by adding a deoxidant such as silicon and/or aluminium.
The slag is then removed, taking the phosphorus from the charge with it.
If sulphur removal is required, a second, reducing slag is formed by
adding limestone with fluorspar to keep it fluid and reducing agents such
as powdered ferrosilicon and calcium carbide. The chemistry of the melt is
adjusted by adding carburiser, Fe-Si, Fe-Mn together with Fe-Cr and Fe-Mo
if required. During time under the reducing slag hydrogen and nitrogen
pick-up can occur, so the reducing period should be as short as possible.
The slag is removed before pouring the steel into the ladle. The steel is
finally deoxidised in the ladle with aluminium.
There are many variations of the basic arc steelmaking process. The practice
used depends on the type of steel to be made and the quality of the scrap
steel used for the charge.
Induction furnace melting
The medium frequency coreless induction furnace (Fig. 4.5) is the most
flexible steel melting unit and is widely used in steel foundries. Small sized
scrap can be melted from cold and the furnace can be used for successive
melts of widely differing analyses. Melting is rapid since high power can be
applied. There is a strong stirring action in the molten steel due to the
induced current, so that a slag cover cannot be maintained. For this reason
there is no refining stage, the liquid steel having similar composition to the
charged scrap except for carbon, silicon and manganese which are lost by
oxidation and must be made up to the required levels by adding pig iron, or
other carburisers and ferroalloys. Alloying elements may also be added and
adjustments to temperature can be rapidly made. High alloy steels are
frequently made in the induction furnace since the melting losses of expensive
alloying elements are low. Extra-low carbon stainless steels can be melted
without pick-up of carbon.
Design of the furnace
The principles of design and operation of coreless induction furnaces are
described in Chapter 4, pp. 55–60.
124 Foseco Ferrous Foundryman’s Handbook
Induction furnaces for steel melting may have a melt capacity of up to
6 tonnes. Frequencies of 1000 Hz are usually used up to about 3 tonnes and
500 Hz for larger furnaces, being powered at up to 750 kW per tonne of
capacity. Such furnaces can be started from cold and have a charge-to-tap
time of about 1 hour.
Refractories
The linings for induction furnaces are nowadays usually made of magnesium-
alumina spinel, which can expand or contract on firing. The usual grade is
30% alumina, 70% magnesia which has an expansion sufficient to produce
metal tightness without damaging the coil.
Linings are made from refractory ramming mixes. The grading of the
refractory is important since it controls packing density and sintering. A
grading of around 45% coarse, 10% medium and 45% fines gives the maximum
packing density. The fines control the sintering of the bond which may be
formed by additions of boric acid or boric oxide, often incorporated in a
proprietary ramming mix. Before installing the lining, the coil and its insulation
should be checked for damage. The usual practice with medium frequency
furnaces is to coat the copper coil of the furnace with a layer of ‘mudding’
about 6 mm thick, of a medium to high alumina cement. This remains in
place when the hot face is knocked out. Between this and the hot face is a
layer of ceramic fibre insulation. The furnace bottom is first formed by
pouring in refractory to a depth of 50–60 mm which is rammed to give the
correct depth. The working face is formed by compacting the refractory
behind a steel former concentrically placed within the coil. Formers are
normally constructed from mild steel sheet according to the furnace
manufacturer’s design. Refractory is poured between the former and the
coil and compacted using vibratory ramming tools or manual compaction
adding more refractory as compaction proceeds. The top layer of the lining
is usually finished by mixing the granular lining refractory with sodium
silicate.
The former is left in the furnace and melted out with the first heat. Power
is slowly increased giving time for the bond to form before the former
melts.
Charge materials
The composition of steel melted in the induction furnace changes little during
melting so that careful selection of charge materials is necessary. Scrap should
be clean, often shot blasted to remove sand, and free from oil and moisture
which may cause hydrogen pick-up and fume. The scrap is charged together
with non-oxidisable alloys. When melted, the oxidisable alloys are added
and the melt brought to the required temperature then tapped as quickly as
Melting and treatment of steel for casting 125
possible. Holding the melt at high temperature should be avoided to minimise
hydrogen pick-up which occurs quite rapidly above 1600°C.
The recycling of scrap in an induction furnace can lead to the pick-up of
gases since no refining takes place. Where possible, scrap from induction
furnaces should be returned to arc furnaces for refining.
AOD refining
AOD refining (argon oxygen decarburisation) has been developed to process
alloy steels for demanding applications. The metal is melted in a primary
arc or induction furnace then transferred to a special AOD vessel with a
controlled slag cover. Oxygen diluted with argon is then injected through a
tuyere at the bottom of the vessel. By reducing the partial pressure of oxygen,
carbon can be removed to low levels without oxidising the chromium and
other elements in the melt. Removal of S and P by slag/metal reaction is
aided by the vigorous stirring of the bath induced by the gas injection.
Steel with precise chemistry can be produced using AOD but at high cost
since the extra vessel is expensive and refractories must be replaced frequently.
It is not widely used in steel foundries outside the USA.
Melting and casting quality
Aspects of casting quality affected by melting and steelmaking practice
include
Deoxidation effects
Sulphides
Inclusions
Gas porosity
Hot tearing
Deoxidation
Liquid steel dissolves oxygen; as the steel cools, the dissolved oxygen combines
with carbon in the steel forming carbon monoxide:
[C] + [O] = CO (g)
If allowed to occur during solidification this would cause gas porosity in
the castings. The amount of dissolved oxygenin the liquid steel depends on
the carbon content of the melt, low carbon steel containing higher oxygen.
The dissolved oxygen is also affected by the silicon and manganese content
of the steel. To avoid gas evolution during solidification, the melt must be
deoxidised with an element which combines preferentially with the dissolved
126 Foseco Ferrous Foundryman’s Handbook
oxygen forming a stable oxide. Silicon, calcium silicide, titanium, zirconium
and aluminium are commonly used deoxidants with aluminium being the
most powerful. Ferrosilicon, calcium silicide or aluminium may be used as
a ‘block’ in the furnace before tapping but the use of aluminium for the final
deoxidation of liquid steel is practically universal.
The addition is usually made in the ladle. Aluminium is commonly used
in stick form for rapid solution. Additions vary from about 0.1% for medium
carbon steel to 0.2% for low carbon steel. Recovery is between 35 and 80%.
Mechanical feeding of aluminium wire is also used, precise control of the
addition is possible since the wire is fed rapidly deep into the melt giving
predictable yields. It is important to control the residual aluminium left in
the melt after deoxidation. Too little may allow the formation of harmful
forms of sulphide and intergranular AlN. Too much will harmfully affect
the steel properties. While aluminium is a powerful deoxidant, the products
of deoxidation are solid crystalline inclusions which are slow to separate
from the molten steel. They reduce the fluidity of the steel and have a
tendency to precipitate in the nozzle bore, reducing the rate at which steel
discharges from the ladle.
CaO fluxes alumina and controls the shape and size of the oxides allowing
them to float out more effectively in the casting ladle. It is difficult to introduce
sufficient calcium into the steel because when a lump of calcium alloy contacts
molten steel, most of the calcium boils off before it has a chance to enter the
steel where it can be effective. Calcium silicide cored wire may be added to
the ladle using a mechanical wire injector. In this way the calcium is introduced
deep into the steel where the ferrostatic head suppresses the rapid vaporisation
of calcium so that it is more effective than bulk additions. Removal of
inclusions is more effective if the steel is ‘rinsed’ with argon after the calcium
treatment through a porous diffuser in the ladle.
Sulphides
As the tensile strength of the steel increases, so the harmful effect of sulphur
increases. In carbon steel castings, 0.06%S may be tolerated but in aircraft
specifications sulphur is limited to 0.02%max. Careful selection of charge
materials is necessary to ensure low sulphur in induction melted steels.
Sulphur is soluble in liquid steel but on solidification it precipitates as MnS.
The sulphides formed may be globular, chain and film, or angular and are
known respectively as Types I, II or III. Type II sulphides are the most
harmful and must be avoided since they seriously affect the Charpy V-
notch values of the steel.
The form of the sulphides is related to the residual aluminium content of
the steel after deoxidation. The least harmful Type I globular sulphides are
formed when residual Al is very low, but this is difficult to control in practice.
The harmful Type II sulphides form at intermediate residual Al levels while
the less harmful Type III angular sulphides are formed at higher residual Al
Melting and treatment of steel for casting 127
levels. The carbon content of the steel also affects the amount of residual Al
needed to ensure Type III sulphides. Low carbon steel requires higher residual
Al (Table 10.1).
Table 10.1 Residual Al% needed to ensure
formation of Type III sulphides in steels of
different carbon content
C (%) Residual Al(%)
0.1 0.04
0.2 0.03
0.3 0.02
0.4 0.02
0.5 0.02
From Jackson & Hubbard p. 235.
Steels with carbon above 0.5% should be deoxidised with 0.04% Al to ensure
100% type III sulphides. The aluminium addition must be increased as the
carbon decreases but the addition should not be too high or the impact
properties may suffer. Steels with carbon contents below 0.2% may
advantageously be deoxidised using Al plus calcium silicide.
Inclusions
Inclusions in steel castings can arise from slag entrapment or from the erosion
of furnace or ladle linings and refractories. They also arise from deoxidation,
being either direct deoxidation products or products arising from reaction
of the killed steel with refractories. For example manganese in killed steel
will reduce the silica in siliceous refractories, the MnO so formed has a
severe fluxing action on firebrick refractories.
Reoxidation of steel during teeming is also a source of inclusions. It has
been estimated that in each pouring or tapping operation, 1–4 kg of oxide
are produced for each tonne of steel transferred. Systems of shrouding the
metal stream with an inert gas have been developed but are not very effective.
The use of calcium silicide in conjunction with controlled additions of
aluminium and argon rinsing are considered effective in reducing inclusions
but can be expensive. Filtration of liquid steel using ceramic foam filters,
(see Chapter 18) is now widely used to reduce the presence of inclusions in
steel castings.
Gas porosity
Gas porosity in steel castings can be attributed to one or both of the following
reactions:
128 Foseco Ferrous Foundryman’s Handbook
[C] + [O] = CO (g) (1)
 2[H] = H2(g) (2)
A reaction similar to (2) is possible for nitrogen.
To minimise porosity, the hydrogen and nitrogen contents of the liquid
steel must be minimised and the carbon/oxygen reaction prevented by a
sufficiently strong deoxidation practice.
Hydrogen
The hydrogen level at which gas holes occur varies according to deoxidation
practice and steel composition. A casting can be made sound as follows:
up to 9 ppm of hydrogen for silicon killed steel castings
9–13 ppm hydrogen for Si and Al killed steel castings
over 13 ppm hydrogen, impossible to obtain solid castings
Hydrogen in liquid steel arises from contact with moisture, usually from
damp refractories and additives. Excessive bath temperatures and prolonged
refining periods should be avoided. All late additions should be dry and
ladles should be thoroughly dried. High atmospheric humidity is a factor
since it may lead to moisture pick-up from refractories (and later from the
sand moulds). A new furnace lining may cause excessive hydrogen pick-up
and it is good practice to melt a ‘wash heat’ before the first charge proper.
Nitrogen
The main source of nitrogen in steel is the atmosphere and the nitrogen
content of the steel depends to a large extent on the length of time that the
bath is in contact with the atmosphere. While nitrogen alone can contribute
to porosity, its normal level is far below the limit of solid solubility. In
0.10%C plain carbon steel castings, when nitrogen is at the 0.013% level,
there is a distinct tendency towards porosity. Nitrogen together with hydrogen
can sometimes be the cause of porosity in high alloy steels, particularly
those containing large amounts of chromium, if high nitrogen ferrochromium
has been used.
Nitrogen pinholes occur in castings made in moulds made using nitrogen-
containing resins such as UF-furanes and phenolic urethanes, and it is
important to use low nitrogen binders, particularly when reclaimed sand is
used (see Chapter 13).
In addition to the possibility of causing porosity, nitrogen in combination
with aluminium may influence the ductility of the steel due to intergranular
fracture caused by AlN precipitating at grain boundaries as the steel cools
through the temperature range 800–900°C. In commercial steel castings, the
minimum amounts of nitrogen combined as aluminium nitride that can
give rise to intergranular fracture are 0.002% for low alloy steels and 0.004%
for plain carbon steels. It is not generally practical to reduce nitrogen to
Melting and treatment of steel for casting 129
such alow level. However, if there is a large enough excess of aluminium in
the steel after deoxidation, AlN can form in the melt and act as nuclei for
precipitation in the solid state. The large AlN particles so formed do not
give rise to intergranular fracture.
Carbon monoxide
The more thorough the deoxidation of the steel, the less the pinholing tendency,
and proper deoxidation with aluminium is the most effective control. There
must be an excess of deoxidant to compensate for the higher oxygen content
that develops in the surface layer of a casting as it comes in contact with the
mould wall. It is possible for silicon and aluminium to be removed locally
which may result in pinhole porosity.
Hot tearing
Hot tearing is a common foundry problem caused by the contraction of the
steel on freezing being hindered by the mould or cores. Chemical composition
of the steel affects hot tearing in a minor way, sulphur having the greatest
effect. Lowering sulphur to below 0.02% can be beneficial in carbon and low
alloy steels, and a manganese content of 0.7–1.3%Mn ensures that any sulphur
present precipitates as MnS rather than the Fe-FeS eutectic which increases
the tendency to hot tear. In high alloy steels, austenitic 18/8 steels do not
tear as severely as plain carbon or 13%Cr steels. As in the case of carbon
steels, sulphur has the greatest adverse effect and manganese improves tear
resistance.
Since hot tearing is caused by mechanical restraint preventing metal
shrinkage occurring, casting design changes, such as use of adequate fillets
at junctions, can be of great help. The minimum binder should be used in
cores and moulds for any casting susceptible to the problem.
The above description of the melting and treatment of steel for casting is
far from complete and for further details the book Steelmaking for Steelfounders,
by W.J. Jackson and M.W. Hubbard, published in 1979 by the Steel Castings
Research and Trade Association, Sheffield is recommended. Thanks are due
to the Castings Development Centre, 7 East Bank Road, Sheffield for
permission to use data from this book and from Steel Castings Design Properties
and Applications referred to above.
Chapter 11
Molten metal handling
Iron foundries
Metal handling systems
The aim of the metal handling system is to deliver clean liquid metal to the
mould at the required temperature. Automatic pouring systems are used
increasingly, but manual pouring is still the commonest method of filling
moulds. Iron foundries almost always use lip-pouring ladles although bottom-
pouring may be used for very large castings such as ingot moulds.
For efficient energy use, molten metal tapping temperature should be as
near as practicable to the desired pouring temperature, having regard to
unavoidable heat losses. In general this is achieved by:
Use of the largest ladle size practicable for pouring moulds.
Ladles should always be covered.
Use of transfer ladles should be avoided, if possible.
Avoid intermittent use of pouring ladles.
Use efficient ladle-heating to prepare ladles for use and when unavoidable
delays occur.
Bucket type ladles with insulated covers lose less heat than drum-type
ladles.
Each transfer of liquid iron from one ladle to another results in a temperature
loss of about 10–20°C.
Ladle lining
The ladle lining in an iron foundry is normally expected to last for a full
shift, in which time it may be used between 50 and 100 times. The lining
material must therefore be of good quality and be applied carefully.
Traditionally, iron foundry ladles have been lined with ganister (crushed
silica rock), naturally bonded sand or firebrick or a combination of these
materials.
Ganisters are usually pre-mixed with a clay binder and are applied with
the minimum amount of water, using a removable former of metal or wood.
Molten metal handling 131
If ladles are used daily on high production plants, the old lining should be
removed completely from the ladle body, which should then be coated
lightly with a ganister wash and the new lining material rammed into position
round the former. The material must be properly vented, by hanging rods
between the ladle shell and the lining. These are removed before drying to
allow easy passage of steam from the lining.
Good quality naturally bonded sand may be used as an alternative to
ganister but the bottom of the ladle should preferably be either brick or
ganister lined to withstand the erosion during filling. The lip and rim of the
ladles are also best lined with ganister. Again, venting is necessary to assist
drying.
Larger ladles are lined with silica firebrick faced with a layer of ganister.
CO2/silicate sand linings may also be used, they are applied using a
former and cured by gassing. Because the free moisture is low, less drying
is needed before use.
The greater the capacity of the ladle, the thicker should be the lining.
Typical thicknesses are:
Ladle capacity (kg) Thickness (mm)
500 25–50
500–5000 50–75
over 5000 75–150
Linings can be damaged by incorrect drying. Properly designed ladle heaters
are better than simple gas-torches. The initial drying must be slow, to avoid
cracking, the gas flame can be increased in intensity as the lining heats up.
When the ladle is completely dry, it is ready for pre-heating. The lining
temperature should be raised to about 900–1000°C before filling with molten
metal. Heat losses are greatest when the ladle is filled for the first time after
pre-heating or if it is only used intermittently, since heat from the metal is
used in heating the refractories to temperature. If ladles are used continuously,
temperature losses stabilise to a predictable value as heat is lost by radiation
from the metal surface and by conduction through the ladle.
The actual cooling rate for any ladle depends on factors such as:
Capacity; larger ladles cool more slowly
Shape; narrow, deep ladles lose less heat by radiation from the metal
surface
How full the ladle is; the fuller, the less the heat loss
The use of covers; a properly fitted cover can halve the cooling rate.
Typical temperature losses from open bucket ladles, well-lined and full are:
Capacity 25 kg 100 kg 500 kg 30 tonnes
Temp. loss 30°C/min 10°C/min 6°C/min <2°C/min
132 Foseco Ferrous Foundryman’s Handbook
These figures are only a rough guide, for greater accuracy, actual
measurements should be made on the ladles in use. The use of a cover will
approximately halve temperature losses.
Heat losses can be reduced by covering the surface of the metal with an
insulating layer (note that it is not desirable to leave slag or dross on the
surface because of the possibility of metal/slag reaction). RADEX 460L
refractory insulator has been developed for this purpose, it is insulating
and inert, having low carbon content and is virtually aluminium free. The
metal should be skimmed clean and a layer of RADEX 460L scattered over
the surface to give a layer about 10 mm thick, or roughly 1.5 kg/tonne of
iron, though this depends on the ladle shape.
KALTEK ladle lining system for iron foundries
The KALTEK system uses a thermally insulating material as a liner to reduce
the time taken to prepare foundry ladles and to provide consistent pouring
temperatures (Fig. 11.1). Pre-heating of ladles is eliminated and installation
is quick and easy. One-piece moulded KALTEK liners are available for many
sizes of iron ladles. The lining is designed to fit accurately into the ladle
shell. A permanent safety lining may sometimes be used as well. A coarse
grained sand (10–20 AFS) is recommended to back-fill the lining to ensure
adequate venting as the organic binders in the liner system burn out. A
sodium silicate bonded core sand, adequately vented, can be used as a sand
cap.
When molten metal is first poured into a cold ladle lined with KALTEK,
heat is absorbed by the lining, which initially causes the metal to cool. On
successive fills, the lining quickly reaches steady state and the cooling becomes
less. Cooling of the metal in the ladle isless than in conventionally lined
ladles because of the insulating properties of the KALTEK material. When
used for iron casting, the life of the lining depends on the metal grade, slag
type and pouring temperature but is usually several hundred fills, allowing
multi-shift use. After use, the one piece lining is easily removed by breaking
the sand cap and overturning the ladle. Cooling is usually unnecessary and
the ladle can be relined immediately. To complement the KALTEK system,
a one-piece insulating lid made from PROCAL can be used to reduce
temperature losses even further.
Two-piece KALTEK ladle liners are available for sizes larger than can be
moulded as a single liner. For even larger ladles, linings can be formed from
KALTEK boards, supplied in the form of segments and bottom boards (Fig.
11.2). The ladle must be furnished with a permanent base lining of alumina
or firebrick to act as a safety lining. The KALTEK segments and base boards
are fitted inside the permanent lining, joints being filled with KALSEAL
refractory cement. The gap between the KALTEK and the permanent lining
is filled with coarse, dry silica sand, 15 AFS is recommended, or BAKFIL.
Multiple filling is possible as long as the ladle lining is not allowed to cool
down between fillings.
Molten metal handling 133
Figure 11.1 Installation of the KALTEK one-piece ladle liner
(a) Coarse grade sand (or BAKFIL) is placed in the base of the ladle
(b) The KALTEK liner is placed in position.
(c) The gap between the KALTEK lining and the shell is filled with coarse
(10–20 AFS) sand
(d) A rammable material such as sodium silicate bonded sand, adequately vented,
seals the top
(e) The FOSCAST refractory dam board is fitted and sealed
(a)
(b)
(d)
(e)
(a)
(c)
(d)
(e)
134 Foseco Ferrous Foundryman’s Handbook
Comparison of KALTEK cold ladle lining system with
conventional ladle lining
A ductile iron foundry making automotive castings in the weight range 1 kg
to 40 kg (average 5 kg) used pouring teapot ladles of 1100 kg capacity lined
with high quality refractory concrete poured around an internal former,
dried and fired with gas burners. Ladles were cleaned and repaired daily,
each ladle had a lifetime of about 500 tonnes of liquid iron. The pouring
practice was
Figure 11.2 Panel ladle made using KALTEK boards.
Molten metal handling 135
Time t = 0 Tap 1100 kg of liquid iron from the furnace to
the treatment ladle
Time t = 2 minutes Transfer to the pouring ladle with inoculation
into the metal stream
Time t = 5 minutes Begin pouring
Time t = 16 minutes End pouring and coat the ladle lip with graphite
wash
Back to t = 0 Repeat cycle, two ladles are in use simultaneously
The cycle remained the same when the foundry changed from using concrete
liners to using the KALTEK cold disposable liner system. For trials, a panel
ladle was made using KALTEK boards (Fig. 11.2). This was later replaced
by a shaped KALTEK two-piece lining (Fig. 11.3) with capacity 1100 kg. The
new ladle lining consisted of three elements: a bottom bowl, a top ring and
a concrete dam plate. Installation of the lining involved:
The bottom bowl was laid on a coarse sand bed
A refractory glue joint was deposited on the horizontal joint
The top ring was installed on the glue joint
The gap between the KALTEK lining and the shell was filled with coarse
(15 AFS) sand
The top of the sand was sealed with a rammable material to prevent sand
leakage when the ladle was tilted. The rammed material was vented by
1 mm holes, 50 mm apart
Figure 11.3 1100 kg capacity teapot KALTEK ladle.
136 Foseco Ferrous Foundryman’s Handbook
After several years of experience with the KALTEK ladles a comparison of
the two lining processes showed:
Furnace temperature reduced by 20°C with the same average pouring
temperature
Less wear of the furnace refractory lining
Lower variance of pouring temperature
Lower ladle shell external temperature, better working environment
Lower direct labour costs on lining operations
Less gas consumption for preheat
Savings in FeSiMg alloy additions because of the lower tap temperature
Significant reduction in non-metallic inclusions
Better process control
KALTEK insulating lining system for
automatic pouring boxes
Many automatic pouring systems, such as the DISAMATIC system, use
refractory lined pouring boxes using a clay-graphite stopper rod and graphite
nozzle. The box has a capacity of 1800 kg with an average fill of 600–900 kg.
The conventional pouring box is lined with a 70% alumina castable having
a life of about 25 shifts with a certain amount of patching needed daily. The
nozzle requires maintenance every 1–11/2 hours to remove slag and metal
build-up.
The KALTEK insulating board system consists of three components:
A back-up refractory safety liner in the metal shell of the pouring box
KALTEK boards custom-designed to fit the safety liner
Coarse sand to separate the KALTEK boards from the safety liner
The stopper rod, nozzle and pouring procedure remain the same.
The back-up 50% alumina liner is cast into the metal shell, since it has no
direct contact with the molten metal, it lasts for years without maintenance.
The KALTEK boards are supplied as custom-fitted sides, ends and bottom
(Fig. 11.4). Metal banding is used to secure the assembled board set until
placement in the pouring box. Before the boards are placed into the box, the
graphite nozzle is set into the nozzle well and secured with a graphitic,
thermally setting, ramming mix.
25 mm of coarse sand is spread evenly across the box floor and the pre-
assembled KALTEK set lowered into the box (Fig. 11.5). More sand is poured
into the cavity between side boards and safety liner. A refractory lid is
attached and any exposed sand capped with a thin layer of plastic ram,
vented with small holes to vent gases arising from organic binders in the
boards. Finally the nozzle is finished according to standard practice.
The lining requires no heating before use, a small gas torch is used to
Molten metal handling 137
preheat the stopper rod and nozzle prior to the first cast. Pouring and
casting are carried out as standard.
Benefits of the KALTEK lining system, in a ductile iron foundry, are:
30°C lower holding temperature
Alloy usage reduced because of lower holding temperature
Rate of heat loss one-third as fast
Refractory costs lowered
Labour costs lowered
Reduction of slag defects, misruns and shrinkage defects
Gas costs drastically lowered
Zero nozzle maintenance
Casting defects due to poor ladle maintenance
Slag and dross inclusions
These arise from slag carried over from the melting furnaces, from slag
deposits left in the ladles after pouring and from fusion of the ladle lining
material. They can be reduced by:
Figure 11.4 Custom fitted KALTEK boards for DISAMATIC automatic pouring system.
Figure 11.5 Lowering the pre-assembled KALTEK boards into the DISAMATIC
automatic pouring box.
138 Foseco Ferrous Foundryman’s Handbook
removal of adhering slag before use;
with tea-pot ladles, molten slag should be removed by back-tilting, to
avoid contamination of the spout;
use of good quality ganister and other lining materials.
Hydrogen pinholing
Caused by molten metal being poured from improperly dried ladles or
damp furnace launders. Hydrogen from the moisture is dissolved in the
liquid metal and released during solidification. The problem is increased by
trace amounts of aluminium in the metal. The defect is avoided by correct
ladle drying and pre-heating.
The use of the KALTEK ladle lining system avoids the above problems.
Adding alloy additions in the ladle
Silicon and molybdenum additions can be made to cast iron by adding
LADELLOY fluxed additives.
SILICON LADELLOY 33 is a fluxed ladle addition allowing the silicon
content of the iron to be increased quickly and accurately. The amount of
silicon to be added is determined by a wedge/chill test. SILICON LADELLOY
33 contains about 62% Si with a flux to ensure optimum pick-up. The required
quantity of additiveis slowly poured into the metal stream as it passes
down the launder to the ladle. The use of ladle additions simplifies melting
operations since a standard charge can be adjusted at the ladle to cover a
wide variety of requirements.
MOLYBDENUM LADELLOY 33 contains about 66%Mo and a small
amount of flux to ensure optimum pick-up of the element. The required
number of units should be placed in the bottom of the ladle and metal
tapped onto them. The phosphorus content of the iron must be less than
0.2% to avoid the formation of molybdenum phosphide.
Molten metal handling in steel foundries
Ladle practice
There are three types of ladle used for steel casting: lip pour, teapot and
bottom pour.
Lip pour ladles
In this type of ladle the metal is discharged over the lip, flow is controlled
Molten metal handling 139
by tilting the ladle using a geared handwheel (Fig. 11.6a). Since the metal
flows from the top of the ladle, the metal surface must be slag-free or a
skimmer must be used to prevent slag entering the mould. The advantages
of lip pouring ladles are that there are no narrow passages in which the
metal can freeze so they are ideal for handling small quantities of metal.
They are used for pouring small steel castings. They are inexpensive easy to
prepare and are immediately ready for use. The disadvantage is that slag
can easily be entrained in the metal stream.
Lifting bail
Safety catches
in open position
pouring stream
Liquid metal
Mild steel shell
Refractory lining
Figure 11.6a Section through a lip pour ladle. (From Jackson, W.J. and Hubbard,
M.W., Steelmaking for Steelfounders, 1979, SCRATA. Courtesy CDC.)
Teapot ladles
A refractory dam before the ladle lip ensures that metal is drawn from the
bottom of the ladle so that the stream is slag free (Fig. 11.6b). Deoxidation
products have more time to float away from the area where metal is being
140 Foseco Ferrous Foundryman’s Handbook
withdrawn so the steel is generally cleaner than from a lip pour ladle. The
disadvantage is that the narrow ‘spout’ may occasionally permit the liquid
steel to freeze if the heat is tapped cold or pouring is prolonged.
Figure 11.6b Section through a teapot ladle. (From Jackson, W.J. and Hubbard,
M.W., Steelmaking for Steelfounders, 1979, SCRATA. Courtesy CDC.)
With both lip pour and teapot ladles, it is only necessary to invert the
ladle to remove all slag and metal before refilling or reheating.
Bottom pour ladles
The ladle is fitted with a pouring nozzle in its base, closed by a refractory
stopper rod (Fig. 11.6c). The metal is drawn from the bottom and is therefore
slag-free and non-metallics such as deoxidation products are able to float
out of the melt. The metal stream flows vertically downwards from the
ladle so that there is no movement of the stream during pouring. The
Lifting bail
Safety catches
in open position
Liquid metal
Mild steel
shell
Refractory lining
Pouring stream
Slag
Molten metal handling 141
disadvantage is that the velocity and rate of flow change during pouring as
the ferrostatic head changes.
Figure 11.6c Section through a bottom pour ladle. (From Jackson, W.J. and Hubbard,
M.W., Steelmaking for Steelfounders, 1979, SCRATA. Courtesy CDC.)
Slag
Liquid metal
Refractory lining
Mild steel shell
Slide
Pouring handle
Stopper rod
Stopper rod covers
Stopper rod end
Pouring nozzle
Unless a reusable system is fitted, the nozzle and stopper rod assembly
must be changed after each use, thereby increasing the turn-round time,
costs and the number of ladles required to handle a given output of metal.
The stopper rod may also distort or erode making it impossible to shut off
the stream completely. It is not practical to handle less than 100 kg of steel
due to the chilling effect of the stopper rod assembly. The flow from a
bottom pour ladle depends on the size of the nozzle and the height of metal
in the ladle so the flow rate and velocity of the metal stream reduces as the
ladle empties. The nozzle/stopper rod is an excellent on-off valve but is not
an effective flow control valve. Attempts to use it to control flow result in
breakup of the metal stream with consequent risk of reoxidation of the steel.
However it is possible to calculate the discharge rate and metal velocity for
each ladle and nozzle and its variation throughout the pour so that ladles
can be suited to the mould sizes that are being cast (see Chapter 18).
142 Foseco Ferrous Foundryman’s Handbook
Ladle linings
The ideal lining is highly refractory, non-reactive with metal or slag and of
low thermal conductivity and heat capacity. Fireclay is the traditionally
used material either in the form of pre-fired bricks or as a plastic ramming
grade. Brick linings must be installed by skilled personnel to ensure tight
joints. Monolithic refractories are easier to install and eliminate the weak
spots associated with bricks.
Although fireclay is the lowest cost refractory, it is possible to raise the
level of as-cast quality considerably by using better lining materials. High
alumina monolithic linings are popular because of their better refractoriness
and their longer life.
Whether bricks, rammed monolithic refractories or castables are used,
there is a long preparation and drying time needed. New ladle linings must
be dried before use to remove moisture. After preliminary air drying, gas
heaters are used to heat the lining to 600–800°C. Final firing of the lining
occurs during its first use.
Steel rapidly loses temperature when held in ladles. A 5-tonne bottom
pouring ladle lined with fireclay will lose 20°C in 5 minutes, while the same
ladle lined with high alumina refractory will lose as much as 50°C in 5
minutes.
The KALTEK ladle lining system
The KALTEK range of products are disposable, insulating, refractory ladle
linings for steel, iron and non-ferrous applications. The low thermal mass
and insulating properties of KALTEK linings eliminate the need for pre-
heat in virtually all ladle sizes and with most alloys. KALTEK inner linings
can be quickly stripped and replaced when necessary.
KALTEK one-piece ladle linings are used for lip pouring in a wide range
of ladle sizes. A FOSCAST castable alumina dam board can be integrated
with the KALTEK liner to create a teapot ladle. Larger ladles, up to 15
tonnes, are lined with KALTEK in the form of board segments and bottom
boards designed to suit individual ladles. KALTEK boards and linings are
supplied in silica based refractory and also alumino-silicate for severe
applications and high magnesia for special alloys.
The ladle to be lined with a pre-formed one piece lining must be free
from holes. The KALTEK one-piece lining is fitted inside the shell with a
minimum of 15 mm backfill of coarse, dry silica sand or BAKFIL, a coarse
graded aggregate (AFS 35). The top exposed ring between lining and shell
should be capped with a suitable mixture such as silicate bonded core sand
and adequately vented with holes every 10–12 cm formed using 6 mm wire
(Fig. 11.1).
Larger ladles to be lined with KALTEK boards must first be stripped and
then furnished with a permanent base lining of alumino silicate bricks or
Molten metal handling 143
castable refractory to act as a safety lining. The permanent lining must be
dried and fired carefully. Vent holes in the ladles must be cleaned or new
holes bored where necessary of 6–8 mm diameter at 20 cm centres.
The KALTEK segments and base boards are then carefully fitted inside
the permanent lining, the joints between them being filled with KALSEAL
refractory cement. The gap between the refractory and backing brick safety
lining should be filled with BAKFIL or coarse, dry silica sand (Fig. 11.2).
Refractory nozzle assemblies can be fitted into bottom pouring KALTEK
lined ladles using special KALPACK ramming material (Fig. 11.7). The nozzle
must be pre-heated to dry the KALPACK product before use.
(3) Modified ladle
nozzle is raised so
that its top is flush
with KALTEK lining
(4) Ladle with nozzle
well-blockas (3) but KALTEK
is butted to well-block
rather than nozzle
Permanent
lining
Backfill Nozzle KALPACK
The four methods available for a bottom pour ladle are shown here:
(1) Normal ladle
nozzle is flush with
permanent lining
(2) Normal ladle
nozzle raised using
packing pieces
Figure 11.7 Methods of installing nozzles in bottom pour ladles.
KALTEK ladle linings are used under cold start conditions, pre-heating
is unnecessary and would destroy the binder components of the boards.
The thermal capacity of a KALTEK lined ladle is lower than conventional
refractories and the thermal insulation twice as good so that while there is
some initial chill when steel is tapped into the cold ladle, the superior
insulation properties soon compensate so that lower tapping temperatures
are possible (Fig. 11.8).
Initially, the concept of the KALTEK cold ladle lining system for steel
foundries was based on single use of the disposable lining, but now in most
cases, multiple life is possible. Pot ladles can be used many times as long as
they are not allowed to cool between fillings. In many cases, bottom pour
ladles can be used more than once as long as multi-life stopper rods such as
the Roto-rod isostatically pressed one-piece alumina-graphite rod are used.
With KALTEK there is:
Various configurations in bottom pour ladles
144 Foseco Ferrous Foundryman’s Handbook
Te
m
pe
ra
tu
re
 °
C
1700
1650
1600
1550
Heat loss comparison
5 ton bottom pour ladle
(steel tapped from AOD vessel)
Tapped at 1693°C
Tapped at 1650°C
KALTEK
No preheat
70% AI2O2
Brick-Preheated
to 800°C
0 5 10 15 20
Time (minutes)
Figure 11.8 Heat loss comparison, 5 ton bottom pour ladle, KALTEK v. brick-lined.
No pre-heat
Faster ladle turnaround
Easier ladle maintenance
Better temperature control
Better working environment
Lower inclusion levels
Pouring temperature for steels
The temperature at which steel castings are poured is at least 50°C above
the liquidus temperature. Further superheat is needed to allow for cooling
Table 11.1 Variation of liquidus temperature with carbon content for Fe-C alloys
Carbon Liquidus temperature Carbon Liquidus temperature
(%) (°C) (%) (°C)
0.05 1533 0.55 1490
0.10 1528 0.60 1486
0.15 1524 0.65 1483
0.20 1520 0.70 1480
0.25 1515 0.75 1477
0.30 1511 0.80 1473
0.35 1507 0.85 1470
0.40 1502 0.90 1466
0.45 1498 0.95 1463
0.50 1494 1.00 1459
Molten metal handling 145
Table 11.2 Depression of liquidus temperature caused by the presence of 0.01% of
alloying elements
Element Depression (°C) Element Depression (°C)
P 0.300 Mo 0.020
S 0.250 Si 0.080
Mn 0.050 Cu 0.050
Cr 0.015 Sn 0.080
Ni 0.040 V 0.030
Example: a steel containing
0.06C, 1.0Si, 1.2Mn, 0.03P, 0.02S, 18Cr, 2.0Mo, 10.5Ni would have a liquidus temperature of
1532 – (8.0 + 6.0 + 0.90 + 0.50 + 27 + 4 + 42) = 1532 – 88.4 = 1444°C
The pouring temperature should be at least 1444 + 50 = 1494° say 1500°C
in the ladle during casting, which can be as high as 10°C per minute in high
alumina lined ladles though much lower for KALTEK lined ladles.
The liquidus temperature of a steel can be estimated from Tables 11.1 and
11.2.
Chapter 12
Sands and green sand
Silica sand
Most sand moulds and cores are based on silica sand since it is the most
readily available and lowest cost moulding material. Other sands are used
for special applications where higher refractoriness, higher thermal
conductivity or lower thermal expansion is needed.
Properties of silica sand for foundry use
Chemical purity
SiO2 95–96% minimum The higher the silica the more
refractory the sand
Loss on ignition 0.5% max Represents organic impurities
Fe2O3 0.3% max Iron oxide reduces the refractoriness
CaO 0.2% max Raises the acid demand value
K2O, Na2O 0.5% max Reduces refractoriness
Acid demand value 6 ml max High acid demand adversely
to pH4 affects acid catalysed binders
Size distribution
The size distribution of the sand affects the quality of the castings. Coarse
grained sands allow metal penetration into moulds and cores giving poor
surface finish to the castings. Fine grained sands yield better surface finish
but need higher binder content and the low permeability may cause gas
defects in castings. Most foundry sands fall within the following size range:
Grain fineness number 50–60 AFS Yields good surface finish at
Average grain size 220–250 microns low binder levels
Fines content, below 2% max Allows low binder level to be
200 mesh used
Clay content, below 0.5% max Allows low binder levels
20 microns
Size spread 95% on 4 or 5 screens Gives good packing and
resistance to expansion defects
Specific surface area 120–140 cm2/g Allows low binder levels
Dry permeability 100–150 reduces gas defects

Sands and green sand 147
Grain shape
Grain shape is defined in terms of angularity and sphericity. Sand grains
vary from well rounded to rounded, sub-rounded, sub-angular, angular
and very angular. Within each angularity band, grains may have high, medium
or low sphericity. The angularity of sand is estimated by visual examination
with a low power microscope and comparing with published charts
(Fig. 12.1).
Figure 12.1 Classification of grain shapes.
High
sphericity
Medium
sphericity
Low
sphericity
Very angular Angular Sub-angular Sub-rounded Rounded Well rounded
The best foundry sands have grains which are rounded with medium to
high sphericity giving good flowability and permeability with high strength
at low binder additions. More angular and lower sphericity sands require
higher binder additions, have lower packing density and poorer flowability.
Acid demand
The chemical composition of the sand affects the acid demand value which
has an important effect on the catalyst requirements of cold-setting acid-
catalysed binders. Sands containing alkaline minerals and particularly
significant amounts of sea-shell, will absorb acid catalyst. Sands with acid
demand values greater than about 6 ml require high acid catalyst levels,
sands with acid demand greater than 10–15 ml are not suitable for acid
catalysed binder systems.
Typical silica foundry sand properties
Chelford 60 Sand (a sand commonly used in the UK as a base for green sand
and for resin bonded moulds and cores)
148 Foseco Ferrous Foundryman’s Handbook
Grain shape: rounded, medium sphericity
Bulk density, loose: 1490 kg/m3 (93 lb/ft3)
GF specific surface area: 140 cm2/g
Angle of repose: 33°
Chemical analysis:
SiO2 Fe2O3 Al2O3 K2O Na2O CaO TiO2 Cr2O3 LOI
97.1 0.11 1.60 0.73 0.15 0.10 0.06 15 ppm 0.3
Acid demand (number of ml 0.1N HCl):
to: pH3 pH4 pH5 pH6 pH7
ml: 2.0 1.8 1.4 1.0 0.8
Sieve grading of Chelford 60 sand
Aperture size (µm) BSS mesh No. % wt retained
1000 16 nil
700 22 0.4
500 30 2.3
355 44 10.0
250 60 25.7
210 72 23.8
150 100 28.7
105 150 7.6
75 200 1.3
–75 –200 0.2
AFS Grain Fineness No. 59
Base permeability: 106
Table 12.1 gives size gradings of typical foundry sands used in the UK and
Germany.
Safe handling of silica sand
Fine silica sand (below 5 microns) can give rise to respiratory troubles.
Modern foundry sands are washed to remove the dangerous size fractions
and do not present a hazard as delivered. It must be recognised, however,
that certain foundry operations such as shot blasting, grinding of sand covered
castings or sand reclamation can degrade the sand grains, producing a fine
quartz dust having particle size in the harmful range below 5 microns.
Operators must be protected by the use of adequate ventilation and the
wearing of suitable face masks.
Sands and green sand 149
Segregation of sand
Segregation, causing variation of grain size, can occur during sand transport
or storage and can give rise to problems in the foundry. The greatest likelihood
of segregation is within storage hoppers, but the use of correctly designed
hoppers will alleviate the problem.
1. Hoppers should have minimum cross-sectional area compared to height.
2. The included angle of the discharge cone should be steep, 60–75°.
3. The dischargeaperture should be as large as possible.
Measurement of sand properties
Acid demand value
Acid demand is the number of ml of 0.1 M HCl required to neutralise the
alkali content of 50 g of sand.
Weigh 50 g of dry sand into a 250 ml beaker
Add 50 ml of distilled water
Add 50 ml of standard 0.1 M hydrochloric acid by pipette
Stir for 5 minutes
Allow to stand for 1 hour
Table 12.1 Typical UK and German foundry sands
Sieve size Sand type
UK sands German sands
microns BSS No. Chelford 50 Chelford 60 H32 H33 F32
1000 16 trace nil
700 22 0.7 0.4
500 30 4.5 2.3 1.0 0.5 1.0
355 44 19.8 10.0 15.0 7.5 7.0
250 60 44.6 25.7 44.0 30.0 30.0
210 72 21.6 23.8 39.0 60.0 60.0
150 100 8.2 28.7
100 150 2.6 7.6
75 200 nil 1.3 1.0 2.0 2.0
75 –200 nil 0.2 nil nil nil
AFS grain fineness No. 46 59 51 57 57
Average grain size 0.275 mm 0.23 0.27 0.23 0.23
Note: Haltern 32, 33 and Frechen 32 are commonly used, high quality German sands.
German sieve gradings are based on ISO sieves.
The German sands have rounder grains and are distributed on fewer sieves than UK
sands, they require significantly less binder to achieve the required core strength.
150 Foseco Ferrous Foundryman’s Handbook
Titrate with a standard solution of 0.1 M sodium hydroxide to pH values
of 3, 4, 5, 6 and 7
Subtract the titration values from the original volume of HCl (50 ml) to
obtain the Acid Demand Value
Grain size
See Section I, pp. 15, 16 for the method of measuring average grain size and
AFS grain fineness number.
Thermal characteristics of silica sand
Silica sand has a number of disadvantages as a moulding or coremaking
material.
It has a high thermal expansion rate (Fig. 12.2) which can cause expansion
defects in castings, such as finning or veining and scabbing.
It has a relatively low refractoriness (Table 12.2) which can cause sand
burn-on, particularly with steel or heavy section iron castings.
It is chemically reactive to certain alloys; for example, ferrous alloys
containing manganese. The oxides of Mn and Fe react with silica to form
low melting point silicates, leading to serious sand burn-on defects.
Figure 12.2 Thermal expansion characteristics of zircon, chromite and olivine
sands compared with silica sand. (Courtesy CDC.)
Li
ne
ar
 e
xp
an
si
on
 (%
)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
200 400 600 800
Temperature (°C)
Silica
Olivine
Chromite
Zircon
For certain types of casting, it may be necessary to use a non-silica sand,
even though all other sands are more expensive than silica.
Sands and green sand 151
Non-silica sands (Table 12.3)
Table 12.3 Properties of non-silica sands (compared with silica)
Property Silica Zircon Chromite Olivine
AFS grain size No. 60 102 74 65
Grain shape rounded rounded angular angular
Specific gravity 2.65 4.66 4.52 3.3
Bulk density (kg/m3) 1490 2770 2670 1700
(lb/ft3) 93 173 167 106
Thermal expansion 1.9% 0.45% 0.6% 1.1%
20–1200°C non-linear
Application general refractoriness resistance to Mn steel
chill metal
penetration
chill
Zircon, ZrSiO4
Zircon sand has a high specific gravity (4.6) and high thermal conductivity
which together cause castings to cool faster than silica sand. The chilling
effect of zircon sand can be used to produce favourable thermal gradients
that promote directional solidification giving sounder castings. The thermal
expansion coefficient of zircon is very low (Fig. 12.2) so that expansion
defects can be eliminated. Zircon has higher refractoriness than silica,
moreover it does not react with iron oxide, so sand burn-on defects can be
avoided. Zircon sand generally has a fine grading, with AFS number between
140 and 65 (average grain size 115–230 microns), the most frequently used
grade is around AFS 100.
Zircon is probably the most widely used of the non-silica sands. It is used
with chemical binders for high quality steel castings and for critical iron
castings such as hydraulic spool valves which contain complex cores, almost
totally enclosed by metal, making core removal after casting difficult. Zircon
has low acid demand value and can be used with all chemical binder systems.
The Cosworth casting process uses the low thermal expansion of zircon
sand cores and moulds to cast dimensionally accurate castings. The high
cost of zircon sand makes reclamation necessary and thermal reclamation
of resin bonded moulds and cores is frequently practised.
Table 12.2 Sintering points of silica sand
Sand Sintering point (°C)
High purity silica sand, >99% quartz 1450
Medium purity silica sand, 96% quartz 1250
Sea sand (high shell content) 1200
Natural clay bonded sand 1050–1150
152 Foseco Ferrous Foundryman’s Handbook
Zircon sands contain low levels of naturally occurring radioactive materials,
such as uranium and thorium. Any employer who undertakes work with
zircon mineral products is required, by law, to restrict exposure of workers
to such naturally occurring contaminants so far as reasonably practical. The
primary requirement is to prevent the inhalation of zircon dust. Suitable
precautions are set out in the UK in HSE Guidance Note EH55: Dust –
general principles of protection. Guidance on the possible hazards associated
with the use, handling, processing, storage, transport or waste disposal of
such naturally occurring radioactive materials and the control measures
that are recommended to minimise exposure should be obtained from the
supplier.
Chromite, FeCr2O4
The high specific gravity (4.5) and high thermal conductivity of chromite
provide a pronounced chilling effect. Thermal expansion is low so expansion
defects are unlikely to occur. Chromite sand has a glossy black appearance,
it has greater resistance to metal penetration than zircon in spite of its
generally coarser grading (typically AFS 70). It has somewhat higher acid
demand than other sands which entails greater additions of acid catalyst
when furane resin is used. Apart from this the sand is compatible with all
the usual binder systems. Chromite is generally used for steel casting to
provide chilling. It is difficult to reclaim chromite sand since, if it becomes
contaminated with silica, its refractoriness is seriously reduced.
Olivine, Mg2SiO4
Olivine sand is used mainly for the production of austenitic manganese
steel castings (which react with silica and other sands to give serious burn-
on defects). It has also been used to avoid the health hazards possible with
silica sand. Olivine has a very high acid demand and is not suitable for use
with acid catalysed binders such as furan resins, it tends to accelerate the
curing of phenolic urethane binders. Being a crushed rock, it is highly angular
and consequently requires high binder additions. Thermal expansion is
regular and quite low.
Green sand
The earliest method of bonding sand grains to form a sand mould was to
use clay and water as a binder. The moulds could be used in the ‘green’ or
undried state (hence the term green sand moulding) or they could be baked
in a low temperature oven to dry and strengthen them to allow heavy
castings to be made. Nowadays, dried, clay bonded sand is little used,
Sands and green sand 153
having been replaced by chemically bonded sand, but green sand is still the
most widely used moulding medium, particularly for iron castings. 40 years
ago, 90% of all steel castings were produced in green sand moulds but this
has now declined and the majority of steel castings are now made in chemically
bonded sand moulds. This reflects the declining tonnage of high volume
repetition steel castings now being made.
Originally, naturally occurring clay-sand mixtures were used, containing
10% or more of clay. It was found that by adding coal dust, the ease of
stripping iron castings from the mould and the surface finish of the castings
could be greatly improved. The heating of the coal dust by the liquid iron
causes the formation of a type of carbon called lustrous carbon which is not
wetted by the liquid iron, so the cast surface is improved. Coal dust additives
are not used forsteel casting since they would cause unacceptable carbon
pick-up on the casting surface.
Clay bonded moulding sand can be used over and over again by adding
water to replace that which is lost during casting, and re-milling the sand.
However, clay which is heated to a high temperature becomes ‘dead’, that
is it loses its bonding power. The coal dust is partly turned to ash by heat,
so new clay, coal dust and water must be added and the sand re-milled to
restore its bonding properties. As the sand is re-used, dead clay and coal
ash build up in the sand, reducing its permeability to gases so that eventually
water vapour and other mould gases are unable to escape from the mould
and defective castings are produced.
Natural sands are little used nowadays (except for some aluminium
castings) and most iron foundry green sands are ‘synthetic’ mixtures based
on washed silica sand to which controlled additions of special moulding
clays (bentonites) and low ash coal dust are made. Alternatively, special
blended additives such as BENTOKOL or CARSIN, which combine the clay
binder with lustrous carbon formers, can be used. Steel foundry green sands
contain bentonites, starches and dextrins. The moulding sand becomes a
‘sand system’ which is continuously recycled, with suitable additions and
withdrawals made as required. The control of system sand to achieve constant
moulding properties has become an important technology of its own for it
determines the quality of the castings produced.
Green sand additives
Base sand: Silica sand of AFS grain size 50–60 is usually used. The particle
size distribution is important, a sand spread over 3 to 5 consecutive sieve
sizes with more than 10% on each sieve gives the best results (see Table
12.1). Rounded or sub-angular sands are the best since the more round the
grains, the better the flowability and permeability of the sand. The base
sand should have the same size grading as the core sand used in the foundry,
so that burnt core sand entering the system does not alter the overall size
grading.
154 Foseco Ferrous Foundryman’s Handbook
Clay: The best bonding clays are bentonites which can either have a calcium
or a sodium base. Sodium bentonites occur naturally in the USA as Wyoming
or Western bentonite and also in other countries particularly in the
Mediterranean area. Green sand produced with this clay has medium green
strength and high dry strength which increases the resistance to erosion of
metal but can give problems at shakeout. Sodium bentonites are commonly
used for steel casting production.
Calcium bentonites are more widely distributed, they produce green sands
with rather high green strength but low dry strength so they have low
erosion resistance and are prone to scabbing and other expansion defects.
Calcium bentonites can be converted to sodium bentonite by adding soda
ash, the calcium base is replaced by sodium and the clay then has properties
approaching those of natural sodium bentonite. Such clays are known as
activated clays.
Blended or mixed bentonites are commercial blends of sodium bentonite
with calcium bentonite or a sodium-activated bentonite. Compositions can
be varied to suit particular applications. Most iron foundries use blended
bentonites.
Clays absorb water from the atmosphere so they should be stored in dry
conditions, they do not deteriorate on storage, even for long periods.
Coal dust: Used mainly in iron foundries with some being used in non-
ferrous foundries. The formation of ‘lustrous carbon’ from the thermal
degradation of the volatiles given off during casting improves casting surface
finish and strip. Good coal dust has the following properties:
Volatile content: 33–36%
Ash: less than 5%
Fixed carbon: 50–54%
Sulphur: less than 1%
Chlorine: less than 0.03%
Size: 75 or 100 grade (AFS grain fineness No.)
It is important that the size grading of the coal dust used should not be too
fine. Coal dust increases the moisture requirement of the sand and the finer
it is, the more moisture is needed, which may have harmful effects on the
castings. Fine coal dust will also reduce the overall permeability of the
sand. Coal dust levels in green sand vary from 2 or 3% for small castings to
7 or 8% for heavy section castings. Too much coal dust can give rise to gas
holes in the castings or misruns.
Coal dust must be stored dry to prevent the risk of fire. Damp coal dust
can ignite spontaneously. Large stocks are undesirable and stocks should be
rotated; first in, first out.
Coal dust replacements: Consist of blends of high volatile, high lustrous carbon
materials blended with clays. They are generally more environmentally
acceptable than coal dust, producing less fume during casting. They can be
Sands and green sand 155
designed for particular applications such as high pressure moulding.
BENTOKOL and CARSIN additives are blends of natural clays to which
have been added specially selected essential volatiles to provide both bond
and volatile content for iron foundry green sand. They are in powder form,
virtually dust free with flow properties and bulk densities similar to clay,
they are supplied in bulk. Use of BENTOKOL/CARSIN often means that a
‘one shot’ sand addition is sufficient and always improves working conditions.
Fume after casting is reduced and the foundry is cleaner and pleasanter
while casting finish is maintained or enhanced.
Many of the BENTOKOL/CARSIN formulations contain a blend of natural
sodium bentonite which has high burn-out temperature and results in lower
concentrations of dead clay. This improves permeability, reduces moisture
requirements and gives better all-round sand properties over a longer life
cycle. Sodium bentonites take longer than other clays to develop their bond.
To offset this BENTOKOL/CARSIN formulations may include dispersion
agents so that the clay is rapidly spread and the bond quickly developed.
BENTOKOL/CARSIN is compatible with sand systems based on clay and
coal dust. Certain parameters of the sand system may change with the
establishment of BENTOKOL/CARSIN; there may be a slight reduction of
volatiles, LOI and clay fraction and the optimum moisture content will fall
by up to 0.5%.
BENTOKOL 80 is a high volatile : clay ratio sand conditioner for the
production of iron castings where exceptional surface finish is required. It
is suitable for use in high pressure or boxless moulding lines. It is a free
flowing grey powder. Because of its high volatile content, one part of
BENTOKOL 80 can usually replace 1.8 parts of coal dust and will additionally
replace a proportion of the clay addition. The use of BENTOKOL 80 ensures
a positive and rapid response to addition rate changes so allowing immediate
alteration of sand properties to match changes in production rate or pattern
mix.
LUCIN is a coal dust replacement product having no bentonite.
Cereal binders: Used mainly in steel foundries to increase strength and
toughness of the green sand. There are two main types of cereal binder:
starch and dextrin. Starch is the basic material and is produced from a
number of plant materials with maize starch being the most commonly
used for foundry purposes. Starch is treated by heating to form ‘pre-gelatinised
starch’ for foundry use. In this form it develops a gel when mixed with
water at about 10% concentration. Dextrin is produced by treating starch
with a weak acid and cooking at 120–150°C. The starch is re-polymerised
and converted to dextrin which is freely soluble in water, forming syrups.
Starch and dextrin additions affect the bonding and moulding properties
of green sand mixtures (Table 12.4).
The main benefits to moulding properties obtained by adding a cereal
binder are:
Providing greater toughness to the mix and, therefore, the compacted
156 Foseco Ferrous Foundryman’s Handbook
Table 12.4 The effect of starch and dextrin on green sand mixes
Property Starch addition Dextrin addition
Green strength Increases moderately Increases slightly
Toughness Increases moderately Increasesmarkedly
Green deformation Increases Increases
Pattern stripping Improves Improves markedly
Mould compaction Little effect Can improve compaction
with high pressure moulding
Sensitivity to change Lowered Lowered
in moisture
Dry strength Increases slightly Increases markedly at
higher moisture content
Friability of mould Increases slightly Markedly reduces
surfaces
From SCRATA Technical Bulletin No. 16, Additives to Green Sand.
sand can deform more easily without fracture, i.e. the cereals correct
the brittleness of the sand. This enables the sand (mould) to strip from
difficult pockets in the pattern without failing. Starch and dextrin are
both effective in this way.
Providing harder and less friable mould surfaces and edges where green
sand moulds are allowed to air dry. Starch is not effective for this
purpose but dextrin, being water soluble migrates to the mould surface
forming a hard, less friable crust. Friable mould surfaces can cause
dirty moulds and sand inclusions in the casting and dextrin corrects
friability problems.
Effect of cereal binders on casting surface quality
Cereal additions do not improve the erosion resistance of the sand or resistance
to metal penetration. They are very good anti-scabbing agents and the higher
the amount of starch or dextrin the greater is the resistance to expansion
scabbing. Starch is more effective in preventing expansion scabbing than a
dextrin and should be employed when making larger green sand moulds
and where radiation effects from the rising steel are most severe.
Use of cereals in moulding mixes
Effective additions of cereal binders to new green sand facing mixes are
between 0.5 and 0.75%. Accurate weighing of the cereal addition is a primary
requirement as is efficient mulling to develop the full properties of the
relatively tough mixes.
In unit type green sands part of the cereal is destroyed during the casting
process. Cereal binders lose their beneficial properties when heated beyond
Sands and green sand 157
225°C. A recommended addition on each recycle is 0.1 to 0.25% depending
upon the amount of cereal burn-out and the dilution by cores and new
sand.
Choice of the type of cereal binder to use depends upon the intended
purpose for the green sand in the foundry. Dextrin is to be preferred for
general green sand work and where moulds air dry before pouring. Starch
is best for larger work where expansion scabbing is possibly a more serious
problem. As a compromise and to give the beneficial effects from both
types, a percentage of starch and dextrin should be added to the moulding
mixes. A suitable proportion is two-thirds starch to one-third dextrin.
Water: Water is needed to develop the clay bond but it can cause casting
defects. Where there is strong, localised heating, e.g. in the vicinity of ingates
or on horizontal mould surfaces exposed to radiant heat from the metal,
moisture is driven back from the mould surface, condensing in a wet, weak
underlying layer that can easily fracture to produce expansion defects in
castings such as scabs, rat-tails and buckles.
MIXAD additive: MIXAD 61 additive has been developed to eliminate sand
expansion defects. By improving the wet strength of the condensed water
layer, MIXAD 61 eliminates the associated defects. MIXAD 61 is added
early in the milling cycle, usually 0.5–1.0% is used in the facing sand. If
MIXAD 61 is used in a unit sand system, an addition of 0.05–0.10% is usually
sufficient. MIXAD 61 is used principally in sands for iron and copper base
alloys.
The green sand system
The ‘sand system’ in green sand foundries is illustrated in Fig. 12.3. It
comprises the following items of equipment;
The bulk sand storage hopper
Returned knockout sand is stored in a hopper which ideally has capacity
for about 4 hours of usage. Returned sand is very variable in properties,
since some will have been heated very strongly by the hot metal while sand
which came from the edges of the mould will have been heated very little.
Some mixing of the sand occurs in the storage hopper. It is better to have
several smaller volume hoppers rather than one large unit since mixing of
the return sand is improved. Hoppers should be designed in such a way
that sand flows evenly through without sticking to the walls.
The sand mill
At the mill, the additions of new sand, clay, coaldust and water are made to
the returned sand. Sand mills may be continuous or batch but batch mills
are nowadays preferred because better sand control is possible. Several
158 Foseco Ferrous Foundryman’s Handbook
designs of mill are available, their purpose is to mix the sand and spread the
moistened clay over the surface of the sand grains in order to develop the
bond. Older sand mills used heavy vertically set mulling wheels and plough
blades (Fig. 12.4). A certain optimum milling time is necessary and this has
to be determined for each green sand system and adhered to carefully. Short
milling times underuse the additives and produce sand having low and
variable green strength. Modern sand mills use intensive mixers to develop
the clay bond quickly and efficiently. Whatever type of mill is used, regular
maintenance is essential to ensure that the milling efficiency does not change.
Additions of new sand, clay and coal dust (or coal dust replacement) are
made at the mill. Batch mills use weighed additions while continuous mills
use calibrated feeders to make continuous additions. Water is added, often
via an automatic moisture controller which measures the moisture content
of the sand as it feeds into the mixer batch hopper prior to mixing then
calculates the exact amount of water to be added to the sand batch discharged
into the mixer to bring the moisture to the required level. Prepared sand is
usually passed through an aerator which ‘fluffs up’ the sand before feeding
the moulding machines.
Buffer hopper
A buffer hopper is usually provided before the moulding machines, so that
a moulding machine stoppage does not necessitate running freshly milled
sand straight back to the main hopper.
The moulding machine(s)
These can be jolt-squeeze, high pressure, impact moulding machines etc.
Each has its advantages and each requires special moulding sand properties.
See p. 164.
Casting
The moulds are cast then allowed to cool for a suitable time, often 30–40
minutes, before knocking out the castings. The cooling time not only allows
the castings to solidify completely but also reduces internal stresses within
the casting caused by differential cooling of sections of varying thickness.
Shake-out
The shakeout separates the castings from the sand. It may be a vibrating
grid or a rotating drum, the latter also having a cooling function since water
is sprayed onto the sand in the drum. The shakeout is provided with copious
air extraction, to prevent dust from entering the foundry. This also removes
some fines from the sand and so plays an important part in the control of
the sand system.
Return sand conveyor
Sand from the shakeout contains lumps of partially burnt cores, very hot
burnt core sand, hot moulding sand from near the casting and cooler moulding
sand from the edges of moulds. A magnetic separator removes metallic
Sands and green sand 159
Road
Tanker
Fill
pipes
Clay
Coal
dust
New
sand
Rotary
screen
Fluid bed cooler
Bulk
sand
storage
Sand
weigh
hopper
Moisture
controller
Weigh
Water
in
Mixer
Aerator
Feed
hopper
Prepared sand conveyor
Moulding
machine
Spill sand conveyor
Knockout
Retu
rn sa
nd c
onve
yor
Mag.
Sep.
Water
sprays
E
le
va
to
r
Figure 12.3 Flow diagram for a typical green sand plant. (From Foundryman,
March 1998, p. 102. Courtesy Foundry and Technical Liaison Ltd.)
Figure 12.4 Vertical wheel batch muller. (Sixth Report of Institute Working Group
T30, Mould and Core Production. Foundryman, Feb. 1986.)
Muller wheel
Plough blade
160 Foseco Ferrous Foundryman’s Handbook
particles and water sprays are used to effect some preliminary cooling before
elevation, since very hot sand candamage the elevator.
Screen
The return sand is elevated to a screen where residual core lumps and other
unwanted material are removed before the sand is returned to the hopper.
Non-magnetic metallics are also removed by the screen.
Sand cooling
Hot sand causes problems of excessive moisture loss and condensation of
moisture on patterns and cores, so the returned sand must be cooled. The
only effective way of cooling green sand is by evaporation of water.
Evaporation of 1% water cools the sand by about 25°C, so water is sprayed
onto the sand and air drawn over the sand to evaporate it, either in the
rotary drum shakeout or at the screen or in a specially designed fluidised
bed cooler. Returned green sand cannot be fluidised by air alone. Sand is
delivered onto a screen which is vibrated to transport the sand along it.
Water is added by sprays and evaporated by blowing air through the
perforated screen.
Sand removal or addition
The sand system must have a facility for removal of excess sand, since
foundries making highly cored castings build up the sand level in the system
through the introduction of burnt core sand. Regular addition of new sand
is needed to maintain control of green sand properties.
Green sand properties
Green sand for iron foundries typically has the following properties:
jolt/squeeze high pressure
machines (DISA etc.)
water 3–4% 2.5–3.2%
green strength 70–100 kPa 150–200 kPa
10–15 psi 22–30 psi
compactability 45–52% 38–40%
permeability 80–110 80–100
live clay 5.0–5.5% 6.0–10.0%
volatiles 2.5% 2.0%
LOI 7.0–7.5% 6.0%
Steel foundries use sand having similar properties except for reduced volatiles
and LOI since coal dust is not used.
A typical grading of a sand suitable for iron or steel castings is:
Sands and green sand 161
Control of green sand systems
When iron or steel is poured into green sand moulds, the heat from the
metal drives off some water from the sand and clay, burns some of the coal
dust to coke and ash (in the case of iron), and burns a proportion of the clay
so that its bonding properties are destroyed. Before the sand can be used
again its properties must be restored by removing burnt clay, coal dust and
ash, and milling in new clay, coal dust (or dextrin) and water. The following
additions are usually necessary at the sand mill in order to maintain the
required moulding properties of the sand.
0.3–0.5% of new clay
0.3–0.5% of coal dust (or 0.2% dextrin)
1.5–2.5% of water
In addition, it is desirable to add a proportion (up to 10%) of new silica sand
to the system and to dispose of a corresponding amount of used system
sand. If highly cored work is made, the amount of new sand addition can
possibly be reduced since well-burnt core sand may serve as new sand, but
care must be taken since certain core binder residues (particularly from
phenolic-isocyanate binders) can harm the green sand properties.
The precise amount of the additions that must be made depends on
many factors, including:
The weight and type of castings being made, which affects the burn-out
The amount of core sand entering the system
Whether hold-ups on the moulding line have allowed freshly milled
sand to return directly to the sand hopper
Good sand control depends on carefully monitored experience of the particular
sand system, since every system is different. The normal additions of clay,
coal dust or BENTOKOL/CARSIN at each cycle represent only about 10%
of the total active clay or coal present in the system. It is not possible to
change the total clay or coal dust content quickly since any change in the
Sieve mesh %
size (µm)
710 0.14
500 1.42
355 5.44
250 22.88
212 19.64
150 26.74
106 9.70
75 2.84
pan 1.10
162 Foseco Ferrous Foundryman’s Handbook
addition rate takes about 20 cycles to work its way fully into the system. For
example; an addition of 0.3% clay is usually sufficient to maintain the total
clay level at 3.0%. If the clay addition is increased to 0.4%, the total clay
content after one cycle will only rise to about 3.1% and it will take 20 cycles
(about 1 week) for the full effect of the change of addition to be felt and for
the clay level to rise to around 4.0%.
The operator must find by experience what additions are needed during
normal operation of the foundry to maintain the required physical properties
of the sand; changes will normally only be necessary if some change of
practice has occurred, such as a change to heavier castings, which will cause
more burn-out of clay and coal. A change to more highly cored castings is
likely to result in more burnt core sand entering the system, which will
require greater additions to compensate.
Because sand systems have such built-in inertia, or resistance to change,
the only way that quick changes can be made to the moulding properties of
the sand is by increasing or reducing the addition of water to the sand mill.
This has an immediate effect on sand properties and as long as the other
constituents of the sand are in control, the sand’s mouldability can quickly
be corrected.
Sand testing
Regular testing of the properties of the sand is essential. One or two sand
tests do not truly indicate the condition of the whole sand system, since a
sand sample weighs only about 1 kg and cannot represent the whole 200
tonnes or so of the system. At least five samples should be taken per shift
and measured for moisture, green strength, compactability and permeability.
LOI and volatiles should be measured once per day. Active clay, twice per week.
Records of additions should also be kept:
Weight of clay, coal dust and new sand added each day
Number of moulds made
Weight of iron poured
Weight of used sand removed from the system each day
The three-ram test method developed by the AFS in the 1920s is still widely
used to measure green strength and compactability although it is not really
suitable for sand used in modern high pressure moulding machines. The
AFS ramming test is being replaced by tests on 50 mm diameter specimens
produced by squeeze machines which can reproduce the pressures actually
developed on the mould by the machine that the foundry uses.
Control graphs
Individual figures mean rather little, but daily average sand properties should
Sands and green sand 163
be plotted together with weekly figures of active clay and average additions
of clay, coal dust and new sand. After a few weeks of plotting the data, it
will be possible to draw control lines. Variation within the lines is permissible
but if results appear outside the control lines, then action must be taken
such as increasing or reducing clay or coal or new sand. If action is taken,
it must be remembered that it will be 1 or 2 days before the full effect of the
action will be seen.
The sand properties, moisture, green strength, compactability and
permeability are of first importance and must be maintained. The remaining
graphs are of secondary importance, but provide useful information which
may allow problems to be anticipated. It is also necessary to keep a log book
for the sand system listing information such as:
When the sand mill was maintained
When new sand was added and old sand removed
Changes in foundry practice, such as change of core binder, or change
in type of casting made.
Parting agents
Unless a water-repellent material is present on the pattern surface to prevent
wetting, green sand will tend to stick to the pattern when rammed. This will
cause damage to the mould when the pattern is withdrawn. To prevent this,
it is usual to spray the pattern with a liquid parting agent such as one of the
SEPAROL grades. The frequency of application depends on the type and
quality of the pattern, but every 10th or 12th mould is typical.
Special moulding materials, LUTRON
LUTRON moulding sand is a waterless sand containing mineral oils designed
for use with fine sands to produce a superfine finish in castings such as
name plates, plaques, medallions and other art castings made in aluminium
or copper base alloys.
The ready-mixed LUTRON mouldingsand is based on a very fine sand
(AFS No. 160). The sand has excellent flowability due to the lubricating
properties of the bond. It can be used alone or as a facing sand backed with
normal green sand or other type of sand. If used as a unit sand, the mix can
be reconstituted after casting by adding a compensating amount of LUTRON
binder and milling.
The LUTRON binder can be used with any suitable fine, dry sand; additions
of 10–12% are normally needed.
164 Foseco Ferrous Foundryman’s Handbook
Green sand moulding machines
The moulding machine must compact the green sand evenly around the
pattern to give the mould sufficient strength to resist erosion while liquid
metal is poured, to withstand the ferrostatic pressure exerted on the mould
when full and to resist the expansion forces that occur on solidification of
the iron. Green sand does not move easily under compression forces alone
so that achieving uniform mould strength over a pattern of complex shape
by simply squeezing is not possible. Various combinations of jolting and
vibrating with squeeze applied simultaneously or sequentially have been
used to produce uniform strength moulds at up to 400 moulds per hour.
Green sand moulds have traditionally been made in steel flasks, but flaskless
moulding is now widely used for smaller castings.
Moulding in flasks
The basic principles used are:
Jolt-Squeeze A pattern plate carrying the pattern surrounded by a moulding
flask is fitted onto a jolt piston. Green sand from a hopper above the machine
fills the moulding box loosely. The assembly is raised by the pneumatic jolt
cylinder and allowed to fall against a stop. The jolt action is repeated a pre-
set number of times causing the sand to be compacted to some extent, the
density being highest nearest the pattern plate. Additional compaction is
then provided by a pneumatic or hydraulic squeeze plate (Fig. 12.5a). More
uniform squeeze can be achieved by using compensating squeeze heads
(Fig. 12.5b) which compact the sand more uniformly even though the depth
of sand over the pattern varies.
Vibration-squeeze Instead of a jolt table, the pattern and flask are vibrated
before and during squeezing by a multi-ram head.
Shoot-squeeze A shoot head above the flask contains loose green sand. Opening
a shoot valve allows compressed air stored in a reservoir to travel through
the shoot head causing a column of sand to be shot into the flask where the
kinetic energy of the rapidly moving sand compacts it against the pattern.
A hydraulic cylinder then squeezes the mould to complete the compaction.
Impulse compaction The flask is filled loosely with prepared sand which is
compacted by means of a pressure wave generated by explosion or by
compressed air. Compaction is greatest near the mould surface. Squeeze
pressure may then be applied to compress the back of the mould. Deep
pattern draws are possible with this method.
Vacuum squeeze A partial vacuum is created in the flask surrounding the
Sands and green sand 165
Figure 12.5 Jolt squeeze moulding machine: (a) with solid squeeze head; (b) with
compensating heads. (Sixth Report of Institute Working Group T30, Mould and Core
Production. Foundryman, Feb. 1996.)
Flask
Guide
pin
Anvil
Ram-jolt
piston
Pattern plate
Air cylinder
on stripping frame
Push-off pin
(a)
Jolt squeeze moulding machine
with solid squeeze heads
Compensating head
Stiffener
Guide
pin
Flask
Peen
block
Moulding sand
Pattern
Pattern plate
Anvil
Ram-joit
piston
Air cylinder
on stripping frame
Push-off pin
(b)
Jolt squeeze moulding machine
with compensating heads
Moulding sand
pattern. A metered amount of sand is released into the chamber where the
vacuum accelerates the sand which impacts onto the pattern causing
compaction. A multi-ram head provides high pressure squeeze to complete
the compaction of the mould. The system is suitable for large moulds.
Flaskless moulding
Horizontally parted (match-plate moulding)
A matchplate is a pattern plate with patterns for both cope and drag mounted
on opposite faces of the plate. Both cope and drag halves of the mould are
filled with prepared sand in the machine before being brought together for
the high pressure squeeze with simultaneous vibration to compact the sand.
The completed mould is pushed out of the machine onto a shuttle conveyor.
Moulds can be made at up to 200 per hour.
Vertically parted moulding
The Disamatic flaskless moulding machine introduced in the late 1960s
(now supplied by Georg Fischer Disa) revolutionised green sand moulding,
allowing high precision moulds to be made at up to 350 moulds/hour. The
method of operation is shown in Fig. 12.6. One pattern half is fitted onto the
end of a hydraulically operated squeeze piston with the other pattern half
fitted to a swing plate, so called because of its ability to move and swing
166 Foseco Ferrous Foundryman’s Handbook
1. Sand shot 2. Mould squeeze from 3. Stripping off the swing
two sides squeeze plate
4. Mould close-up and mould
string transport
5. Stripping of the rear
squeeze plate
6. Closing the moulding
chamber
Figure 12.6 Vertically parted flaskless moulding, the Disamatic machine. (Sixth
Report of Institute Working Group T30, Mould and Core Production. Foundryman,
Feb. 1996.)
away from the completed mould. Sand from a supply hopper above the
machine is blown into the moulding chamber by means of a variable pressure
compressed air supply stored in a nearby air receiver. Vacuum can be applied
to the moulding chamber to vent air and assist in drawing sand into deep
pattern recesses. Both halves of the pattern are hydraulically squeezed together
to compress the sand block. As the swing plate moves away, the piston
pushes the new mould to join ones previously made, to form a continuous
mould string. Mould sizes available are from 500 mm × 400 mm × 315 mm
on the smallest 2110 model, up to 950 mm × 800 mm × 635 mm on the largest
model manufactured, the 2070. Flexibility is available through variable mould
output, variable mould thickness, fast pattern change and core placing options.
Varying degrees of control sophistication are provided dependent on the
model. Cores can be placed in the mould using a mechanised core placer.
There are many variations on the moulding principles described above.
See Sixth Report of Institute of British Foundrymen Working Group T30
(Foundryman, Feb. 1996, p. 3) from which some of the above information has
been taken.
Chapter 13
Resin bonded sand
Chemical binders
A wide variety of chemical binders is available for making sand moulds
and cores. They are mostly based either on organic resins or sodium silicate
(see Chapter 14), although there are other inorganic binders such as cement,
which was the earliest of the chemical binders to be used; ethyl silicate,
which is used in the Shaw Process and for investment casting and silica sol,
which is also used for investment casting.
The binders can be used in two ways:
As self-hardening mixtures; sand, binder and a hardening chemical are
mixed together; the binder and hardener start to react immediately, but
sufficiently slowly to allow the sand to be formed into a mould or core
which continues to harden further until strong enough to allow casting.
The method is usually used for large moulds for jobbing work, although
series production is also possible.
With triggered hardening; sand and binder are mixed and blown or rammed
into a core box. Little or no hardening reaction occurs until triggered by
applying heat or a catalyst gas. Hardening then takes place in seconds.
The process is used for mass production of cores and in some cases, for
moulds for smaller castings.
Self-hardening process (also known as self-set,
no-bake or cold-setting process)
Clean, dry sand is mixed with binder and catalyst, usually in a continuous
mixer. The mixed sand is vibrated or hand-rammed around the pattern or
into a core box; binder and catalyst react, hardening the sand. When the
mould or core has reached handleable strength(the strip time), it is removed
from the pattern or core box and continues to harden until the chemical
reaction is complete.
Since the binder and catalyst start to react as soon as they are mixed, the
mixed sand has a limited ‘work time’ or ‘bench life’ during which the mould
or core must be formed (Fig. 13.1). If the work time is exceeded, the final
strength of the mould will be reduced. Work time is typically about one-
168 Foseco Ferrous Foundryman’s Handbook
third of the ‘strip time’ and can be adjusted by controlling the type of
catalyst and its addition rate. The work time and strip time must be chosen
to suit the type and size of the moulds and cores being made, the capacity
of the sand mixer and the time allowable before the patterns are to be re-
used. With some binder systems the reaction rate is low at first, then speeds
up so that the work time/strip time ratio is high. This is advantageous,
particularly for fast-setting systems, since it allows more time to form the
mould or core.
Figure 13.1 Typical hardening curve for self-hardening sand:
Tw = work time
Ts = strip time
Tc = casting time
Tmax = time to achieve maximum strength.
psi kPa
500 3500
80% max
50 350
1.5 10
C
om
pr
es
si
on
st
re
ng
th
Tw Ts Tc Tmax
Time
Stripping is usually possible when the sand has reached a compression
strength of around 350 kPa (50 psi) but the actual figure used in practice
depends on the type of binder system used, the tendency of the binder to
sag before it is fully hardened, the quality of the pattern equipment and the
complexity of the moulds and cores being made.
It is advisable to strip patterns as soon as it is practical, since some binder
chemicals attack core box materials and paints after prolonged contact. The
properties of chemical binders can be expressed in terms of:
Resin bonded sand 169
Work time (bench life): which can be conveniently defined as the time after
mixing during which the sand mixture has a compressive strength less
than 10 kPa, at this stage it is fully flowable and can be compacted easily.
Strip time: which can be defined as the time after mixing at which a
compressive strength of 350 kPa is reached, at this value most moulds
and cores can be stripped without damage or risk of distortion.
Maximum strength: the compressive strength developed in a fully hardened
mixture, figures of 3000–5000 kPa are often achieved.
It is not necessary to wait until the maximum strength has been achieved
before moulds can be cast, the time to allow depends on the particular
castings being made, usually casting can take place when 80% of the maximum
strength has been reached.
Testing chemically bonded self-hardening sands
Units
Compressive strength values may be reported in
SI units kPa = kN/m2
cgs units kgf/cm2
Imperial units psi = lbf/in2
Conversion factors:
100 kPa (kN/m2) = 1.0197 kgf/cm2
= 14.5038 psi (lbf/in2)
1 kgf/cm2 = 98.0665 kPa
= 14.22 psi (lbf/in2)
 1 psi (lbf/in2) = 6.895 kPa (kN/m2)
= 0.07032 kgf/cm2
Conversion table
kPa (kN/m2) kgf/cm2 psi (lbf/in2)
10 0.10 1.5
50 0.51 7.3
100 1.02 14.5
200 2.04 29.0
300 3.06 43.5
400 4.08 58.0
500 5.10 72.5
600 6.12 87.0
700 7.14 101.5
170 Foseco Ferrous Foundryman’s Handbook
800 8.16 116.0
900 9.18 130.5
1000 10.20 145.0
2000 20.39 290.1
3000 30.59 435.1
4000 40.79 580.1
5000 50.99 725.2
The curing properties (work time, strip time and maximum strength) are
measured by compression tests using 50 mm diameter specimen tubes with
end cups, or AFS 2 inch diameter tubes, with a standard rammer. Sand is
mixed in a food mixer or small coresand mixer; catalyst being added first
and mixed, then the resin is added and mixed.
Measurement of ‘work time’ or ‘bench life’
Mix the sand as above, when mixing is complete, start a stopwatch and
discharge the sand into a plastic bucket and seal the lid.
After 5 minutes, prepare a standard compression test piece and immediately
measure the compressive strength.
At further 5 minute intervals, again determine the compressive strength,
stirring the mixed sand in the bucket before sampling it.
Plot a graph of time against strength and record the time at which the
compressive strength reaches 10 kPa (0.1 kgf/cm2, 1.5 psi); this is the work
time or bench life.
The sand temperature should also be recorded.
For fast-setting mixtures, the strength should be measured at shorter
intervals, say every 1 or 2 minutes.
Measurement of strip time
Prepare the sand mixture as before.
When mixing is complete, start a stop-watch.
Prepare 6–10 compression test pieces within 5 minutes of completion of
mixing the sand.
Cover each specimen with a waxed paper cup to prevent drying.
Determine the compressive strength of each specimen at suitable intervals,
say every 5 minutes.
Plot strength against time.
Record the time at which the strength reaches 350 kPa (3.6 kgf/cm2, 50 psi),
this is the ‘strip time’.
The sand temperature should also be recorded.
Measurement of maximum strength
Prepare the sand mixture as before.
Resin bonded sand 171
Record the time on completion of mixing.
Prepare 6–10 specimens as quickly as possible covering each with a waxed
cup.
Determine the strength at suitable intervals say, 1, 2, 4, 6, 12, 24 hours.
Plot the results on a graph and read the maximum strength.
The sand temperature should be held constant if possible during the test.
While compressive strength is the easiest property of self-hardening sand
to measure, transverse strength or tensile strength are being used more
frequently nowadays, particularly for the measurement of maximum strength.
Mixers
Self-hardening sand is usually prepared in a continuous mixer, which consists
of a trough or tube containing a mixing screw. Dry sand is metered into the
trough at one end through an adjustable sand gate. Liquid catalyst and
binder are pumped from storage tanks or drums by metering pumps and
introduced through nozzles into the mixing trough; the catalyst nozzle first
then binder (so that the binder is not exposed to a high concentration of
catalyst).
Calibration of mixers
Regular calibration is essential to ensure consistent mould and core quality
and the efficient use of expensive binders. Sand flow and chemical flow
rates should be checked at least once per week, and calibration data recorded
in a book for reference.
Sand: Switch off the binder and catalyst pumps and empty sand from the
trough. Weigh a suitable sand container, e.g. a plastic bin holding about
50 kg. Run the mixer with sand alone, running the sand to waste until a
steady flow is achieved. Move the mixer head over the weighed container
and start a stop watch. After a suitable time, at least 20 seconds, move the
mixer head back to the waste bin and stop the watch. Calculate the flow
in kg/min. Repeat three times and average. Adjust the sand gate to give
the required flow and repeat the calibration.
Binders: Switch off the sand flow and the pumps except the one to be
measured. Disconnect the binder feed pipe at the inlet to the trough,
ensuring that the pipe is full. Using a clean container, preferably a polythene
measuring jug, weigh the binder throughput for a given time (minimum
20 seconds). Repeat for different settings of the pump speed regulator.
Draw a graph of pump setting against flow in kg/min.
Repeat for each binder or catalyst, taking care to use separate clean
containers for each liquid. Do not mix binder and catalyst together, since
172 Foseco Ferrous Foundryman’s Handbook
they may react violently. Always assume that binders and catalysts are
hazardous, wear gloves, goggles and protective clothing.
When measuring liquid flow rate, the pipe outlet should be at the same
height as the inlet nozzle of the mixer trough, so that the pump is working
against the same pressure head as in normal operation.
Mixers should be cleaned regularly. The use of STRIPCOTE AL applied to
the mixer blades, reduces sand build-up.
Sand quality
In all self-hardening processes, the sand quality determines the amountof
binder needed to achieve good strength. To reduce additions and therefore
cost, use high quality sand having:
AFS 45–60 (average grain size 250–300 microns)
Low acid demand value, less than 6 ml for acid catalysed systems
Rounded grains for low binder additions and flowability
Low fines for low binder additions
Size distribution, spread over 3–5 sieves for good packing, low metal
penetration and good casting surface.
Pattern equipment
Wooden patterns and core boxes are frequently used for short-run work.
Epoxy or other resin patterns are common and metal equipment, usually
aluminium, may be used for longer running work. The chemical binders
used may be acid or alkaline or may contain organic solvents which can
attack the patterns or paints. STRIPCOTE AL aluminium-pigmented
suspension release agent or silicone wax polishes are usually applied to
patterns and core boxes to improve the strip of the mould or core. Care
must be taken to avoid damage to the working surfaces of patterns and
regular cleaning is advisable to prevent sand sticking.
Curing temperature
The optimum curing temperature for most binder systems is 20–25°C but
temperatures between 15 and 30°C are usually workable. Low temperatures
retard the curing reaction and cause stripping problems, particularly if metal
pattern equipment is used. High sand temperatures cause reduction of work
time and poor sand flowability and also increase the problem of fumes from
the mixed sand. If sand temperatures regularly fall below 15oC, the use of
a sand heater should be considered.
Resin bonded sand 173
Design of moulds using self-hardening sand
Moulds may be made in flasks or flaskless. Use of a steel flask is common
for large castings of one tonne or more, since it increases the security of
casting. For smaller castings, below one tonne, flaskless moulds are common.
Typical mould designs are illustrated in Fig. 13.2. The special features of
self-hardening sand moulds are:
Large draft angle (3–5°) on mould walls for easy stripping
Incorporation of a method of handling moulds for roll-over and closing
Means of location of cope and drag moulds to avoid mismatch
Reinforcement of large moulds with steel bars or frames
Clamping devices to restrain the metallostatic casting forces
Use of a separate pouring bush to reduce sand usage
Mould vents to allow gas release
Sealing the mould halves to prevent metal breakout
Weighting of moulds if clamps are not used
Use of minimum sand to metal ratio to reduce sand usage, 3 or 4 to 1 is
typical for ferrous castings
Foundry layout
With self-hardening sand; moulds and cores are often made using the same
binder system, so that one mixer and production line can be used. A typical
layout using a stationary continuous mixer is shown in Fig. 13.3. The moulds
may or may not be in flasks. Patterns and core boxes circulate on a simple
roller track around the mixer. The length of the track is made sufficient to
allow the required setting time, then moulds and cores are stripped and the
patterns returned for re-use.
For very large moulds, a mobile mixer may be used.
Sand reclamation
The high cost of new silica sand and the growing cost of disposal of used
foundry sand, make the reclamation and re-use of self-hardening sands a
matter of increasing importance. Reclamation of sand is easiest when only
one type of chemical binder is used. If more than one binder is used, care
must be taken to ensure that the binder systems are compatible. Two types
of reclamation are commonly used, mechanical attrition and thermal.
Wet reclamation has been used for silicate bonded sand. The sand is
crushed to grain size, water washed using mechanical agitation to wash off
the silicate residues, then dried. The process further requires expensive
water treatment to permit safe disposal of the wash water so its use is not
common.
174 Foseco Ferrous Foundryman’s Handbook
The difficulty and cost of disposing safely of used chemically bonded
sand has led to the growing use of a combination of mechanical and thermal
treatment. Mechanical attrition is used to remove most of the spent binder.
Depending on the binder system used, 60–80% of the mechanically reclaimed
sand can be rebonded satisfactorily for moulding, with the addition of clean
sand. The remaining 20–40% of the mechanically treated sand may then be
(a)
(d)
(b)
(c)
Figure 13.2 Typical designs of self-hardening moulds. (From Foundry Practice
Today and Tomorrow, SCRATA Conference, 1975.) (a) Method of moulding-in steel
tubes for ease of handling boxless moulds. (b) Sockets moulded into boxless moulds
for ease of lifting, roll-over and closing. (c) Steel reinforcement frames for handling
large boxless moulds. (d) Method of locating mould halves and preventing runout.
Resin bonded sand 175
thermally treated to remove the residual organic binder, restoring the sand
to a clean condition. This secondarily treated sand can be used to replace
new sand. In some cases, all the used sand is thermally treated.
Mechanical attrition
This is the most commonly practised method because it has the lowest cost.
The steps in the process are:
Lump breaking; large sand lumps must be reduced in size to allow the
removal of metal etc.
Separation of metal from the sand by magnet or screen.
Disintegration of the sand lumps to grain size and mechanical scrubbing
Mould hardening
Mixer
Empty box return
pattern clean
Roll-over and
stripping
Mould
close
Casting
area
Figure 13.3 Foundry layout for self-hardening sand moulds.
176 Foseco Ferrous Foundryman’s Handbook
to remove as much binder as possible, while avoiding breakage of
grains.
Air classification to remove dust, fines and binder residue.
Cooling the sand to usable temperature.
Addition of new sand to make up losses and maintain the quality of the
reclaimed sand.
Reclamation by attrition relies on the fact that the heat of the casting burns
or chars the resin binder close to the metal. Even at some distance from the
metal, the sand temperature rises enough to embrittle the resin bond. Crushing
the sand to grain size followed by mechanical scrubbing then removes much
of the embrittled or partially burnt binder. The more strongly the sand has
been heated, the more effectively is the sand reclaimed.
Mechanical attrition does not remove all the residual binder from the
sand, so that continued re-use of reclaimed sand results in residual binder
levels increasing until a steady state is reached which is determined by:
the amount of burn-out which occurs during casting and cooling
the effectiveness of the reclamation equipment
the percentage of new sand added
the type of binder used.
The equilibrium level of residue left on the sand is approximately expressed
as:
 
P TB
TR
 = 
1 – 
P is the maximum percentage of resin that builds up in the sand (the LOI
of the reclaimed sand)
B is the binder addition (%)
T is the fraction of binder remaining after reclamation
R is the fraction of sand re-used
Example: In a typical furane binder system
B = 1.4% resin + 0.6% catalyst = 2.0%
T = 0.7 (only 30% of the binder residue is removed)
R = 0.90 (90% of reclaimed sand is re-used with 10% new sand)
P =
 
0.7 2.0
1 – (0.7 0.9)
×
×
= 3.78% (residual binder that builds up on the sand)
This represents an inefficient reclaimer. Ideally P should not exceed 3.0%.
Even with an inefficient reclaimer P = 3% can be achieved by reducing R,
that is, by adding more new sand. For example, reducing R to 0.75 (25%
addition of new sand) reduces P to 2.95%
Regular testing of reclaimed sand for LOI, acid demand, grain size and
Resin bonded sand 177
temperature is needed, together with regular maintenance of the reclaimer
to ensure that consistent mould quality is achieved.
Binder systems containing inorganic chemicals, e.g. silicate based systems,
alkaline phenolic resins or binder systems containing phosphoric acid are
difficult to reclaim at high percentages because no burn-out of the inorganic
material occurs.
Use of reclaimedsand with high LOI may cause problems due to excessive
fumes at the casting stage, particularly if sulphonic acid catalysed furane
resins are used.
Thermal reclamation
Sand bonded with an entirely organic binder system can be 100% reclaimed
by heating to about 800°C in an oxidising atmosphere to burn off the binder
residues, then cooling and classifying the sand. Thermal reclaimers are usually
gas heated but electric or oil heating can also be used. The steps in the
process are:
Lump breaking
Metal removal
Heating to about 800°C for a certain time in a fluidised bed furnace or
rotary kiln
Cooling the sand, using the extracted heat to preheat the incoming sand
or the combustion air
Classification
Addition of new sand to make up losses in the system.
Thermal reclamation is costly because of the large amount of heat needed
and the relatively expensive equipment. The ever growing cost of sand
disposal, however, leads to its increasing use.
Sand losses
Whatever method of reclamation is used, there is always some loss of sand
so that 100% reclamation can never be achieved. Sand losses include: burn-
on, spillage, inefficiencies in the sand system and the need to remove fines.
Dust losses of around 5% can be expected and total sand losses of up to 10%
may be expected.
Typical usage of sand reclamation
Furane bonded sand
Mechanical attrition allows up to 90% of sand to be re-used. Only sulphonic
178 Foseco Ferrous Foundryman’s Handbook
acid catalysed sand can be reclaimed. Reclaimed sand may have up to 3%
LOI. Binder additions on rebonding can be reduced by 0.15–0.2% (from say,
1.2% on new sand to 1.0%) with a proportionate reduction of catalyst. Nitrogen
and sulphur levels build up and may cause casting defects and excessive
fume if allowed to exceed 0.15% when the sand is rebonded. Low nitrogen
resins must be used.
Thermal treatment at 800°C can be used on the residual sand. Nitrogen
and sulphur are removed with the remaining organic content.
Phenolic urethane bonded sand
Up to 90% of sand can be reclaimed by mechanical attrition. If iron oxide is
added to the sand mix, care must be taken to ensure that the iron content of
the sand does not rise too high or the refractoriness may suffer.
Thermal reclamation can be used on the residual sand as long as the iron
oxide content is low.
Cold box core sand, from core assembly casting processes, can be thermally
reclaimed satisfactorily. If uncontaminated core lumps can be separated
from green sand, they can also be reclaimed.
Alkaline phenolic bonded sand
These binders contain potassium which, if allowed to rise above 0.15% in
the reclaimed sand, will cause unacceptable reduction of work time and
final strength. This limits attrition reclamation to about 70%.
The residue after attrition reclamation can be thermally reclaimed if it is
treated with FENOTEC ADT 1, an anti-fusion additive. This additive prevents
sintering of the sand during thermal treatment and aids removal of potassium
salts.
Resin shell sand
Shell moulding and core sand (silica or zircon) is fully reclaimable by thermal
means. The used sand often has as much as 2% of residual resin left after
casting. Useful heat can be obtained from the combustion of the resin residues
which significantly reduces the quantity of heat that must be supplied. The
quality of the reclaimed sand must be regularly checked for:
Size grading
LOI (the visual appearance of the sand, which should be the colour of
new sand, gives a good indication of LOI)
Inorganic residues, e.g. calcium stearate additions, which are often made
to lubricate shell sand, burn to CaO during reclamation, giving rise to
high acid demand.
Foundries wishing to thermally reclaim shell sand must have equipment to
re-coat the sand for re-use.
Resin bonded sand 179
Silicate-ester bonded sand
Standard silicate-ester bonded sand can be reclaimed mechanically only at
rather low levels, less than 50% because the build-up of soda in the sand
reduces its refractoriness. The presence of reclaimed sand in the re-bonded
mix reduces the work time and final strength and increases the tendency for
sagging.
VELOSET special silicate ester binder (see Chapter 14)
Up to 90% reclaimed sand can be re-used with the VELOSET system. Shakeout
sand is reduced to grain size in a vibratory crusher which provides the
primary attrition stage. The sand is then dried in a fluidised bed drier.
Secondary attrition takes place next in a hammer mill. The sand is finally
passed through a cooler-classifier ready for re-use. The reclaimed sand is
blended with new sand in the proportion 75 to 25. During the first 10 cycles
of re-use, the sand system stabilises and the bench life of the sand increases
by a factor of up to 2. Also, mould strength should improve, and it is usually
possible to reduce the binder addition level by up to 20% yet still retaining
the same strength as achieved using new sand. Once the process has become
established, it becomes possible to re-use up to 85–90% of the sand (Figs
14.4, 14.5).
Wet reclamation
Some silicate bonded sands are particularly difficult to reclaim mechanically
because Na2O builds up and lowers refractoriness. (VELOSET sand is an
exception.) Thermal reclamation is ineffective, but water washing can be
used. The steps in the process are:
Lump breaking
Metal separation by magnet or screen
Disintegration to grain size
Water wash with mechanical agitation to wash off the silicate residues
Separation of sand and water
Drying of the sand
Agglomeration of the alkaline residues in the water to allow settlement
and separation
Water treatment to permit safe disposal of the water
Wet reclamation is expensive and its use is not common.
180 Foseco Ferrous Foundryman’s Handbook
Self-hardening resin binder systems
Furanes
Foseco products: FUROTEC, ESHANOL Binders.
Principle: Self-setting furane sands use a furane resin and an acid catalyst.
The resins are urea-formaldehyde (UF), phenol-formaldehyde (PF), or UF-
PF resins with additions of furfuryl alcohol (FA). Speed of setting is controlled
by the percentage of acid catalyst used and the strength of the acid.
Sand: Since the resins are acid catalysed, sands should have a low acid
demand, less than 6 ml.
Resin: A wide range of resins is available having different nitrogen content.
The UF base resin contains about 17–18% N; furfuryl alcohol is N-free, so
the N content of a UF-FA resin depends on its FA content. Nitrogen can
cause defects in steel and high strength iron castings, so it is advisable to
use high FA resins (80–95% FA, 3.5 – 1% N) although they are more expensive
than lower FA resins. These resins are particularly useful with sands of high
quality, such as the German Haltern and Frechen sands, which are round-
grained and can be used with low resin additions (<1.0%) so the total nitrogen
on the sand is low.
A range of UF-PF furanes is also available, having low nitrogen content,
they are frequently used with sands of rather lower quality, which require
quite high resin additions (>1.2%). The total nitrogen on the sand can be
kept to a lower level than is possible with UF-FA resins.
Phenol-formaldehyde resin is N-free and a range of totally N-free PF-FA
resins is available, these are used for particularly sensitive castings, or when
sand is reclaimed. Where the presence of phenol in the resin presents a
problem, due to restrictions on used sand disposal, special phenol-free FA-
Resorcinol resins (FA-R resins) can be used. They contain less than 0.5%N
and are used for steel and high quality iron casting. While they are expensive,
they are used at low addition rates.
Catalyst: UF-FA resins can be catalysed with phosphoric acid, which has the
advantage of low odour and no sulphur but reclamation of the sand is
difficult. FA-R, PF-FA, UF-FA with high FA and UF-PF-FA resins are catalysed
with sulphonic acids, either PTSA (para-toluene sulphonic acid), XSA (xylene
sulphonic acid) or BSA (benzene sulphonic acid), the last two are strong
acids and are usedwhen faster setting is required. Sulphonic acid catalysed
resin sand can be reclaimed but the sulphur content of the sand rises and
may cause S defects in ferrous castings particularly in ductile iron.
Environmental problems may also arise due to the SO2 gas formed when
moulds are cast. Mixed organic and inorganic acids may also be used.
Addition rate: Resin: 0.8–1.5% depending on sand quality. Catalyst: 40–60%
Resin bonded sand 181
of resin, depending on sand temperature and speed of setting required. If
fast setting is required, XSA or BSA catalyst should be used.
Pattern equipment: Wood or resin is commonly used. Metal patterns can be
used but if the pattern is cold, setting may be retarded. FA is a powerful
solvent and will attack most paints, patterns must be clean and preferably
unpainted. Special release agents such as STRIPCOTE AL can be used.
Temperature: The optimum is 20–30°C. Cold sand seriously affects the setting
speed and the final strength.
Strength: Depends on resin type and addition, typically 4000 kPa (600 psi)
compression strength.
Speed of strip: Can be from 5–30 minutes. Short strip times require high
speed mixers and may cause problems of sand build-up on the mixer blades.
Work time/strip time: UF-FA resins are better than PF-FA, the higher the FA
content, the better.
Coatings: Water or spirit based coatings may be used, alcohol based coatings
may cause softening of the mould or core surface and it is advisable to
allow 1/2–1 hour between stripping and coating.
Environmental: Formaldehyde is released from the mixed sand, so good
extraction is needed around the mixer. When sulphonic acid catalyst is
used, SO2 gas is evolved when moulds are cast, particularly if reclaimed
sand is used.
Reclamation: Attrition reclamation works well and it is often possible to
reduce the resin addition on reclaimed sand. Low N resin and sulphonic
acid catalyst must be used. The LOI of the reclaimed sand must be kept to
less than 3.0%. N and S in the sand should not exceed 0.15% when the sand
is rebonded.
Casting characteristics: N above 0.15% in the sand will cause defects in iron
and steel castings. S above 0.15% in the sand may cause reversion to flake
graphite at the surface of ductile iron castings. Metal penetration can be a
problem if work time is exceeded.
General: Probably the most widely used self-hardening system because of
the easy control of set times, good hot strength, erosion resistance and the
ease of reclamation.
182 Foseco Ferrous Foundryman’s Handbook
Phenolic-isocyanates (phenolic-urethanes)
Foseco product: POLISET Binder.
Principle: The binder is supplied in three parts. Part 1 is a phenolic resin in
an organic solvent. Part 2 is MDI (methylene diphenyl diisocyanate). Part 3
is a liquid amine catalyst. When mixed with sand, the amine causes a reaction
between resin and MDI to occur, forming urethane bonds which rapidly
sets the mixture. The speed of setting is controlled by the type of catalyst
supplied in Part 1.
Sand: The binder is expensive, so good quality sand is needed to keep the
cost of additions down. AFS 50–60 is usually used.
Addition rate: The total addition is typically 0.8% Part 1, 0.5% Part 2, more or
less being used, depending on the sand quality.
Pattern equipment: Wood, resin or metal can be used. Paints must be resistant
to the strong solvents in Part 1 and Part 2.
Temperature: Sand temperature affects cure rate, but not as seriously as other
binders. The optimum temperature is 25–30°C.
Speed of strip: Can be very fast, from 2–15 mins. A high speed mixer is
needed to handle the fast cure rates.
Work-time/Strip-time: Very good.
Strength: Compression strength is typically over 4000 kPa (40 kgf/cm2,
600 psi).
Coatings: If water-based coatings are used, they should be applied immediately
after strip and dried at once. Spirit based coatings should be applied 15–20
minutes after strip and are preferably air-dried.
Casting characteristics: Lustrous carbon defects may occur on ferrous castings.
Part 2 (MDI) contains 11.2% N and gas defects may occur in steel castings.
The binder has rather low initial hot strength, so erosion defects may occur.
All these problems can be reduced by the addition of 1 or 2% of iron oxide
to the sand.
Reclamation: Attrition works well, 90% re-use of sand is possible. If iron
oxide is added to the sand mix, care must be taken to ensure that the iron
content of the sand does not rise too high or the refractoriness may suffer.
Environmental: Solvent release during mixing and compaction may be
troublesome, use good exhaust ventilation. Isocyanates can cause respiratory
problems in sensitised individuals. Once an individual has become sensitised,
Resin bonded sand 183
exposure, however small, may trigger a reaction. MDI has very low vapour
pressure at ambient temperature, so exposure to the vapour is unlikely to
cause problems, however uncured isocyanate may be present on airborne
sand particles at the mixing station. Good exhaust ventilation is essential.
General: This system has never been as popular in the UK and Europe as in
the USA due to the difficulty of stripping and the low hot strength. Steel
foundries find it useful for cores, where the low hot strength reduces hot
tearing.
Alkaline phenolic resin, ester hardened
Foseco products: FENOTEC, FENOTEC hardener.
Principle: The binder is a low viscosity, highly alkaline phenolic resole resin.
The hardener is a liquid organic ester. Sand is mixed with hardener and
resin, usually in a continuous mixer. The speed of setting is controlled by
the type of ester used.
Sand: Can be used with a wide range of sands including zircon, chromite
and high acid demand sand such as olivine.
Resin addition: 1.2–1.7% depending on the sand quality; 18–25% hardener
based on resin.
Nitrogen content: Very small or zero.
Pattern equipment: Wood or resin, patterns strip well.
Temperature: Low sand temperature slows the cure rate, but special hardeners
are available for cold and warm sand.
Speed of strip: 3 min to 2 hours depending on the grade of hardener used.
The work time/strip time ratio is good.
Strength: 24 h strength: transverse 1600 kPa 16 kgf/cm2 230 psi
tensile 900 9 130
compression 4000 40 600
Coatings: Some iron and steel castings can be made without coatings. Both
water based and spirit based coatings can be used, but some softening-back
of the sand surface is possible. The stripped core or mould should be allowed
to harden fully before applying the coating. Water based coatings should be
dried as quickly as possible. Alcohol based coatings should be fired as soon
as possible after application.
184 Foseco Ferrous Foundryman’s Handbook
Casting characteristics: Good as-cast finish on all metals. Hot tearing and
finning defects are eliminated. No N, S or P defects. Good breakdown,
particularly on low melt point alloys. Widely used for steel castings as well
as iron and aluminium.
Reclamation: FENOTEC binders allow up to 70–90% sand reclamation by
attrition, there is some loss of strength and careful management of the alkali
content of the reclaimed sand is needed. The remainder of the sand can be
thermally reclaimed if it is treated with FENOTEC ADT 1, an anti-fusion
additive which aids potassium removal.
Environmental: Low fume evolution at mixing, casting and knockout stages.
General: Stripping from all pattern types is excellent; this, together with the
good casting finish achieved and the low fume evolution, makes the system
popular for all types of casting but most of all for steel.
Triggered hardening systems
Cores for repetition foundries are usually made using a triggered hardening
system with the mixed sand being blown into the core box. The cores must
be cured in the box until sufficient strength has been achieved to allow
stripping without damage or distortion, usually the core continues to harden
after stripping. Transverse breaking strength or tensile strength are used to
assess the properties of triggered core binder systems sincethey represent
the properties needed to strip and handle cores. The strength requirements
needed depend on the particular type of core being made. Thin section
cores, such as cylinder head water jacket cores, require high stripping strength
because of their fragile nature. Tensile strengths of 1000–2000 kPa (150–300
psi) are typical, equating roughly to transverse strengths of 1500–3000 kPa.
Final strengths may be higher, but some binder systems are affected by
storage conditions (humidity in particular) and strengths may even fall if
the storage conditions are poor. Surface hardness is also important but difficult
to measure precisely.
Heavy section cores and moulds made by core blowing can be successfully
made with lower strength binders, and factors such as fume released on
casting and compatibility of core residues with the green sand system may
be more important than achieving the very highest strength.
Heat triggered processes
The sand and binder are mixed then introduced into a heated core box or
pattern. The heat activates the catalyst present in the binder system and
cures the binder. Core boxes and patterns must be made of metal, normally
Resin bonded sand 185
grey cast iron, evenly heated by means of gas burners or electric heating
elements. The working surface of the core box is usually heated to 250°C,
higher temperatures may overcure or burn the binder. Sand is a rather poor
conductor of heat and heat penetration is rather slow (Fig. 13.4), it is therefore
difficult to cure thick sections of sand quickly and fully. When the core is
ejected from the core box, residual heat in the sand continues to penetrate
into the core, promoting deeper cure. To achieve the fastest cure times,
heavy section cores are often made hollow, using heated mandrels or ‘pull-
backs’ to reduce core thickness. Core boxes are usually treated with silicone
release agents to improve the strip. The thermal expansion of the metal core
box must be taken into account when designing core boxes. A cast iron core
box cavity 100 mm long will expand by 0.27 mm when heated from 25 to
250°C. This change becomes significant on large cores.
Figure 13.4 Temperature rise in a sand core with one surface in contact with a
heated core box at 250°C (theoretical).
Heating time (s)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
D
ep
th
 (
in
)
50°C
70°C
100°C
16
14
12
10
8
6
4
2
0
0 20 40 60 80 100 120
D
ep
th
 (
m
m
)
Other methods of applying heat to sand cores have been tried. Microwave
or dielectric heating is difficult because electrically conducting metal core
boxes cannot be used. Certain resins can be used for core boxes but they
pick up heat from the cores and may distort.
Blowing heated air through the core has also been used, but a large
volume of air is needed and the method becomes slow and impractical if
core sections above about 30 mm are to be cured. Approximately 1 kg (800
litres at STP) of heated air is needed to heat 1 kg of sand to curing temperature.
186 Foseco Ferrous Foundryman’s Handbook
Gas triggered systems
Sand and binder are mixed and blown into a core box then a reactive gas is
blown into the core box causing hardening of the binder. Hardening occurs
at room temperature, avoiding the need for heated core boxes. Many of the
gases used to trigger chemical reactions are highly reactive and toxic so that
specially designed gas generators are needed to meter the gas accurately
into the core box. Core boxes must be sealed to contain the gases and often
scrubbers must be used to absorb the exhaust gas to prevent it from
contaminating the atmosphere both inside and outside the foundry. Frequently,
the gassing cycle includes an air purge to remove residual gas from the core
so that it can be handled and stored safely.
Gas cured binder systems often allow very fast curing, even of thick
section cores.
Heat triggered processes
The Shell or Croning process
Principle: Sand is pre-coated with a solid phenolic novolak resin and a catalyst
to form a dry, free-flowing material. The coated sand is blown into a heated
core box or dumped onto a heated pattern plate causing the resin to melt
and then harden. Cores may be solid or they may be hollow with the uncured
sand shaken out of the centre of the core. Shell moulds are normally only
20–25 mm thick.
Sand: The base sand is usually a fine silica sand of AFS 60-95. To achieve the
highest strength with the minimum resin addition, the sand should be pure,
rounded grain and free from surface impurities. Zircon sand is also pre-
coated for special applications.
Resin and catalyst additions: The resins are solid phenolic novolaks which
melt at around 100°C. The catalyst is hexamine, a white powder. Resin
additions are 2.5–4.5% (depending on the application and the strength
required), hexamine is added at 11–14% of the resin content.
Nitrogen content: The resins are N-free but hexamine contains 40% N. Special
low N systems with little or no hexamine are available.
Pre-coating procedure: There are two processes; hot coating and warm coating.
In the hot coating procedure, the sand is heated to around 130°C and charged
into a batch mixer. Solid resin granules are added, the heat from the sand
melts the resin which then coats the sand grains. Aqueous hexamine solution
plus release agents are added, cooling the sand below the melt point of the
resin. The coated sand is broken down to grain size and finally cooled.
Resin bonded sand 187
In warm coating, the sand is heated to 50°C and charged into a batch
mixer together with hexamine and release agents. Resin in alcohol solution
is added and warm air blown through the mixer to vaporise the solvent,
leaving the sand evenly coated. After breaking down the sand lumps and
cooling, the coated sand is ready for use.
Many foundries purchase ready coated sand from specialist suppliers.
Bench life: Pre-coated sands last indefinitely if stored dry and not exposed to
excessive heat, which may cause clumping.
Core blowing: The free-flowing sand can be blown at low pressure, 250–350
kPa(35–50 psi). Core boxes should be made of cast iron heated to 250°C.
Copper or brass must be avoided since ammonia released during curing
will cause corrosion.
Curing times: Minimum curing time is 90 seconds but 2 minutes is common.
The longer the curing time, the thicker is the shell build-up. Increasing
curing temperature does little to speed up cure rate and runs the risk of
overcuring the sand adjacent to the core box or pattern plate.
Core strength: Surface hardness and strength is high on ejection. A 3.5% resin
content will give a tensile strength of 1400 kPa (200 psi). Storage properties
of cured cores is excellent.
Gas evolution: 4–5 ml/g of gases for each 1% of resin.
Casting characteristics: Core and mould coatings are unnecessary. The surface
finish of castings is excellent. Breakdown is good, particularly with hollow
cores. Accuracy and reproduction of pattern detail is extremely good because
of the free-flowing properties of pre-coated sand. Some distortion, particularly
of moulds, can occur on casting and support of shell moulds by steel shot
or loose sand may be needed for heavy section castings. N defects may
occur on steel castings unless low-N coated sand is used. Excellent surface
finish is achieved on aluminium castings.
Health hazards: Phenol and ammonia are released during curing so good
ventilation is needed at core and mould making machines. Casting into
shell moulds produces unpleasant and hazardous fumes and often shell
moulds are cooled in an enclosed tunnel, allowing fumes to be collected
and exhausted outside the foundry.
Reclamation: When both moulds and cores are made by shell process, the
sand can be reclaimed thermally.
Shell moulding: Shell moulds are made by dumping pre-coated sand onto an
iron pattern plate heated to 240–260°C. After a suitable time, usually about
2 minutes, the mould is overturned, returning the uncured sand to the
188 Foseco Ferrous Foundryman’sHandbook
hopper and leaving a shell mould 20–25 mm thick which is ejected from the
pattern plate. Cores are placed and the two half-moulds are glued together
with hot-melt adhesive (CORFIX).
Shell moulds are usually cast horizontally, unsupported. If cast vertically,
support is usually necessary to prevent mould distortion. Steel shot is
frequently used to support the mould.
KALMIN pouring cups are often used with horizontally poured shell
moulds.
General: The shell process was one of the first synthetic resin foundry processes
to be developed. Although it is slow and rather expensive, it is still widely
used, because of the excellent surface finish and dimensional accuracy of
the castings produced.
Hot box process
Principle: The binder is an aqueous PF-UF or UF-FA resin, the catalyst is an
aqueous solution of ammonium salts, usually chloride and bromide. Sand
is mixed with the liquid resin and catalyst and blown into a heated core box.
The heat liberates acid vapour from the catalyst which triggers the hardening
reaction. Hardening continues after removal of the core from the box causing
the sand to be cured throughout.
Sand: Clean silica sand of AFS 50-60, acid demand should be low. The binder
is aqueous so traces of moisture in the sand do not affect the cure. Low sand
temperatures (below 20°C) slow the cure rate.
Resin addition: 2.0–2.5% depending on sand quality. Catalyst additions are
20–25% of the resin weight.
Nitrogen content: The resin contains 6–12%N. The catalysts are usually
ammonia chloride solutions and also contain N. The total N in the system
is 10–14% depending on the resin used. Low-N or N-free systems are available
but their performance is not as good as the N-containing binders.
Mixing procedure: Batch or continuous mixers can be used, add catalyst first
then the resin.
Bench life: 1–2 hours, mixed sand must be kept in closed containers to prevent
drying out. High ambient temperatures reduce bench life.
Core blowing: High blowing pressure, 650–700 kPa (90–100 psi) is needed to
blow the wet sand into core boxes.
Core boxes: Cast iron or steel, fitted with gas or electric heaters to maintain
Resin bonded sand 189
the temperature at 250–300°C. Silicone parting agents are usually applied to
improve the strip of the core.
Curing time: Thin section cores cure in 5–10 seconds. As cores increase in
section, curing time must be extended up to about one minute for 50 mm
section. For larger sections still, it is advisable to lighten-out cores with
heated mandrels, otherwise the centre of the core will remain uncured.
Core strength: Surface hardness and strength is high on ejection. Final tensile
strength is 1400–2800 kPa (200–400 psi). Storage properties are good if cores
are kept dry.
Casting characteristics
Ferrous castings: Cores are usually coated to prevent burn-on. Water based
coatings, such as RHEOTEC are used. The hot strength and breakdown is
good, particularly for the UF-PF-FA resins, the higher the PF content, the
worse the breakdown. The rather high nitrogen can cause gas holes and
fissures in iron castings and additions of 1–3% of a coarse grained form of
iron oxide are often used to minimise N-defects. Finely powdered red iron
oxide can also be used but it causes some loss of strength.
Hot box cores made using phenolic resin expand slightly during casting
and this can cause distortion, for example on large water jacket cores. Iron
oxide additions reduce the expansion, so does the use of UF/FA resins.
Aluminium castings: Special hot box resins are available which break
down readily at aluminium casting temperatures.
Copper-base castings: Brass water fittings are commonly made with special
hotbox resin cores.
Health hazards: Formaldehyde is liberated during curing, so coreblowers
and the area around them must be well ventilated and exhausted. Avoid
skin contact with liquid resins and mixed sand.
Reclamation: It is not normal to reclaim hot box cores when they are used in
green sand moulds. Core sand residues in green sand are well tolerated.
General: The hot box process was the first high speed resin coremaking
process. Gas-cured cold box processes have superseded it in many cases,
particularly for thick section cores, but hot box is still used because of its
good surface hardness, strength in thin sections and excellent breakdown
properties.
Warm box process
Principle: The binder is a reactive, high furfuryl alcohol binder. The catalyst
is usually a copper salt of sulphonic acid. Sand, binder and catalyst are
190 Foseco Ferrous Foundryman’s Handbook
mixed and blown into a heated core box. The heat activates the catalyst
which causes the binder to cure.
Sand: Clean silica sand of AFS 50–60 is used. Low acid demand is advisable.
Resin addition: 1.3–1.5% resin and 20% catalyst (based on resin) depending
on sand quality.
Nitrogen content: The resin contains about 2.5% N. The catalyst is N-free.
Mixing procedure: Continuous or batch mixers. Catalyst should be added
first, then resin.
Bench life: Typically 8 hours.
Core blowing: The binder has low viscosity and blow pressures of around
500 kPa (80 psi) may be used.
Core boxes: Cast iron or steel heated to 180–200°C. Use a silicone based
parting agent. A release agent is sometimes added to the sand/binder mix.
Curing time: 10–30 seconds depending on the thickness. Thick section cores
continue to cure after ejection from the core box.
Core strength: Surface hardness and strength is high on ejection. Final tensile
strength can be 3000–4000 kPa (400–600 psi).
Casting characteristics: Gas evolution is low, the low nitrogen content reduces
incidence of gas related defects in ferrous castings. Surface finish of castings
is good with low incidence of veining defects. Breakdown after casting is
good.
Environmental: Emission of formaldehyde is low at the mixing and curing
stages. Avoid skin contact with binder, catalyst and mixed sand.
Reclamation: Core residues in green sand are not harmful.
General: Warm box cores have high strength and resistance to veining and
are used in critical applications, usually for iron castings such as ventilated
brake discs.
Oil sand
Principle: Certain natural oils, such as linseed oil, known as ‘drying oils’,
polymerise and harden when exposed to air and heat. Natural oils can be
chemically modified to accelerate their hardening properties. Silica sand is
Resin bonded sand 191
mixed with the drying oil, a cereal binder and water. The resulting mixture
is either manually packed or blown into a cold core box. The cereal binder,
or sometimes dextrin, gives some green strength to the core which is then
placed in a shaped tray or ‘drier’ to support it during baking. The baking
hardens the oil and the core becomes rigid and handleable.
Sand: Clean silica sand, AFS 50-60.
Binder addition: 1–2% of drying oil
1–2% pre-gelatinised starch or 2% dextrin
2–2.5% water 0.5–1% water
Nitrogen content: Zero.
Mixing: Batch mixers are preferred in order to develop the green bond strength,
mixing times may be 3–10 minutes.
Bench life: As long as the mixture does not lose moisture, the bench life is up
to 12 hours.
Core blowing: Oil sand mixtures are sticky and difficult to blow, the highest
blow pressure possible (around 700 kPa, 100 psi) is used. They are frequently
hand-rammed into core boxes.
Core boxes: May be wood, plastic or metal. Wooden boxes require a paint or
varnish to improve the strip. Metal boxes are preferably made of brass or
bronze to aid stripping of the fragile green cores.
Curing: A recirculating air oven is needed since oxygen is necessary to harden
the oil. The temperature is normally 230°C, allowing 1 hour for each 25 mm
section thickness. Burning and consequent friable edges may occur on thin
section cores, if this happens, a lower temperature for a longer time should
be used.
Core strength: Green strength is low so sagging will occur if the cores are not
supported during baking. Correctly baked cores develop tensile strength of
1340 kPa (200 psi).Casting characteristics: Breakdown after casting is excellent. The gas evolution
is high, particularly if cores are under-baked, venting is often necessary.
Water based coatings can be used. While for most applications, oil sand has
been superseded by synthetic resin processes, it still remains a valuable
process in applications where particularly good breakdown of cores is needed,
for example for high conductivity copper and high silicon iron castings in
which hot tearing is a serious problem.
Health hazards: Unpleasant fumes are emitted during baking and ovens must



192 Foseco Ferrous Foundryman’s Handbook
be ventilated. Some proprietary core oils contain a proportion of mineral
oil, which may be harmful if skin contact is prolonged.
Gas triggered processes
Phenolic-urethane-amine gassed (cold box) process
Foseco products: POLITEC and ESHAMINE cold box resin
Principle: The binder is supplied in two parts. Part 1 is a solvent based
phenolic resin, Part 2 is a polyisocyanate, MDI (methylene di-phenyl di-
isocyanate) is a solvent. The resins are mixed with sand and the mixture
blown into a core box. An amine gas (TEA, triethylamine or DMEA, dimethyl
ethyl amine or DMIA, dimethyl isopropyl amine) is blown into the core,
catalysing the reaction between Part 1 and Part 2 causing almost instant
hardening.
Sand: Clean silica sand of AFS 50–60 is usually used but zircon and chromite
sands can be used. The sand must be dry, more than 0.1% moisture reduces
the bench life of the mixed sand. High pH (high acid demand) also reduces
bench life. Sand temperature is ideally about 25°C, low temperature causes
amine condensation and irregular cure. High temperature causes solvent
loss from the binder, and loss of strength.
Resin addition: Total addition is 0.8–1.5% depending on sand quality. Normally
equal proportions of Part 1 and Part 2 are used.
Nitrogen content: Part 2, the isocyanate, contains 11.2% N.
Mixing procedure: Batch or continuous mixers can be used, add Part 1 first
then Part 2. Do not overmix since the sand may heat and lose solvents.
Bench life: 1–2 hours if the sand is dry.
Core blowing: Use low pressure, 200–300 kPa (30–50 psi), the blowing air
must be dry, use a desiccant drier to reduce water to 50 ppm. Sticking of
sand and resin to the box walls can be a problem due to resin blow-off. The
lowest possible blow pressure should be used. Use of a special release agent
such as STRIPCOTE is advised.
Core boxes: Iron, aluminium, urethane or epoxy resin can be used. Wood is
possible for short runs. Use the minimum vents that will allow good filling,
since reduced venting gives better catalyst gas distribution. The exhaust
vent area should be 70% of the input area to ensure saturation of the core.
Core boxes must be sealed to allow the amine catalyst gas to be collected.
Resin bonded sand 193
Gas generators: The amine catalysts are volatile, highly flammable liquids.
Special generators are needed to vaporise the amine and entrain it in air or
CO2. The carrier gas should be heated to 30–40°C to ensure vaporisation.
Controlled delivery of amine by pump or timer is desirable.
Gas usage: Approximately 1 ml of amine (liquid) is needed per kilogram of
sand. The amine usage should be less than 10% of Part 1 resin. DMEA is
faster curing than TEA. Typical curing is a short gassing time (1–2 seconds)
followed by a longer (10–20 seconds) air purge to clear residual amine from
the core. Over-gassing is not possible but simply wastes amine.
Typical gassing times:
core wt (kg) total gas+purge (s)
10 10
50 30
150 40
Core strength: Tensile strength immediately after curing is high, 2000 kPa
(300 psi), transverse strength 2700 kPa (400 psi). Storage of cores at high
humidity reduces the strength considerably. The use of water based coatings
can cause loss of strength.
Casting characteristics
Ferrous castings Good surface and strip without coatings
Low hot strength but this can be improved by adding
iron oxide
Tendency to finning or veining
Lustrous carbon formation may cause laps and
elephant skin defects on upper surfaces of castings.
Addition of red iron oxide (0.25–2.0%) or a coarse-
grained form of iron oxide at 1.0–4.0% reduces defects
Breakdown is good
The N content may cause problems on some steel
castings.
Aluminium castings Good surface and strip
Poor breakdown, the resin hardens when heated at
low temperature. Aluminium castings may need heat
treatment at 500°C to remove cores
There are no hydrogen problems.
Reclamation: Excessive contamination of green sand with cold box core residues
can cause problems. Cold box cores and moulds can be thermally reclaimed
if uncontaminated with iron oxide.
194 Foseco Ferrous Foundryman’s Handbook
Environmental: TEA, DMIA and DMEA have objectionable smells even at 3
or 6 ppm. Good, well sealed core boxes, good exhaust and good exhaust gas
scrubbers are necessary. The cores must be well purged or amine will be
released on storage. Liquid amine is highly flammable, treat like petrol.
Air/amine mixtures may be explosive. MDI (Part 2) acts as a respiratory
irritant and may cause asthmatic symptoms but it has low volatility at
ambient temperature, and is not normally a problem. Avoid skin contact
with resins or mixed sand.
General: In spite of its environmental and other problems, the cold box
process is so fast and produces such strong cores that it is the most widely
used gas triggered process for high volume core production. Good engineering
has enabled the environmental problems to be overcome. Reduced free-
phenol resins are being produced to assist with sand disposal problems.
The ESHAMINE Plus process
This patented process is a development of the amine gassed phenolic-urethane
cold box process which overcomes the problems of using volatile liquid
amine catalysts. The liquid amines TEA, DMEA and DMIA must be vaporised
to function effectively. Under cold ambient conditions, amine condensation
in the gas supply lines or in the core box itself may occur.
In the ESHAMINE Plus process, a gaseous amine, TMA (trimethylamine)
is used as catalyst. TMA is the most reactive of the tertiary amine family and
has a boiling point of 3°C (compared to 89°C for TEA, 65°C for DMIA and
35°C for DMEA). Being a gas at ambient temperature simplifies the design
of gassing equipment, reduces gas consumption and improves productivity.
Gassing times are reduced by up to 78% and purge times by up to 54%
compared to DMEA, DMIA or TEA catalysed cores. These reductions have
been found to have a significant impact on the overall cycle time of the core
machine, raising core output by 30%. A further benefit of the reduced gas
usage is the lower cost of amine scrubber maintenance.
ECOLOTEC process (alkaline phenolic resin
gassed with CO2)
Foseco product: ECOLOTEC resin
Principle: ECOLOTEC resin is an alkaline phenol-formaldehyde resin
containing a coupling agent. The resin is mixed with sand and the mixture
blown into a core box. CO2 gas is passed through the mixture, lowering the
pH and activating the coupling agent which causes crosslinking and hardening
of the resin. Strength continues to develop after the core is ejected as further
crosslinking occurs and moisture dries out.
Sand: Clean silica sand of AFS 50-60 is used. The sand should be neutral (pH
Resin bonded sand 195
7) with low acid demand. Zircon and chromite sands can be used, but
olivine sand is not suitable. Temperature is ideally 15–30°C.
Resin addition: 2.0–2.5% depending on the sand grade.
Nitrogen content: Zero.
Mixing procedure: Batch or continuous.
Bench life: Curing occurs only by reaction with CO2. The CO2 in the air will
cause a hardened crust on the surface of the mixed sand, but the soft sand
underneath can be used. Keep the mixed sand covered. The bench life is
usually 5 hours at 15°C reducing to 1 hour at 30°C.
Core blowing: Blow pressure 400–550 kPa (60–80 psi) is needed.
Core boxes: Wood, metal or plastic. Clean them once per shift and use SEPAROL
or a silicone based releaseagent.
Gassing: Cores are blown at 400–550 kPa (60–80 psi) then gassed for 20–40
seconds at 100–300 litres/minute. CO2 consumption is about 2% (based on
weight of sand). Gas should not be forced through the core box at high
velocity since the gas must react with the binder. No purge is necessary
before extracting the core.
Core strength
as gassed
(kPa) (kgf/cm2) (psi)
Transverse 800–1000 8–10 110–140
Transverse strength doubles after one hour. Cores should be stored in dry
conditions.
Casting characteristics: Steel, iron, copper based and light alloy castings can
be made. ECOLOTEC is free from N, S and P. Finning and lustrous carbon
defects do not occur. Breakdown after casting is good.
Coating: Water or solvent based coatings can be used without affecting the
strength. Methanol coatings should be avoided.
Environmental: Gassed cores have no odour. Fume is low at mixing, casting
and knockout.
Reclamation: Not normally practised when cores are used in green sand
moulds. The inflow of alkaline salts into green sand can result in strong
activation of the bentonite clay, a move to a partially activated bentonite
will counteract the effect.
196 Foseco Ferrous Foundryman’s Handbook
General: Tensile strength is not as high as the amine gassed isocyanate process
but the excellent casting properties, freedom from nitrogen, lustrous carbon
and finning defects and above all its environmental friendliness make
ECOLOTEC an attractive process particularly for larger cores and moulds
for iron steel and aluminium castings.
The SO2 process
Principle: Sand is mixed with a furane polymer resin and an organic peroxide,
the mixture is blown into the core box and hardened by passing sulphur
dioxide gas through the compacted sand. The SO2 reacts with the peroxide
forming SO3 and then H2SO4 which hardens the resin binder.
Sand: Clean silica sand of AFS 50-60. Other sands may be used if the acid
demand value is low. The temperature should be around 25°C, low
temperature slows the hardening reaction.
Resin addition: Typically 1.2–1.4% resin, 25–60% (based on resin) of MEKP
(methyl ethyl ketone peroxide).
Nitrogen content: Zero.
Mixing: Batch or continuous mixers, add resin first then peroxide. Do not
overmix since the sand may heat and reduce bench life.
Bench life: Up to 24 hours.
Core blowing: Blowing pressure 500–700 kPa (80–100 psi).
Core boxes: Cast iron, aluminium, plastics or wood can be used. A build up
of resin film occurs on the core box after prolonged use, so regular cleaning
is needed by blasting with glass beads or cleaning with dilute acetic acid.
Curing: The SO2 gas is generated from a cylinder of liquid SO2 fitted with a
heated vaporiser. The gas generator must also be fitted with an air purge
system so that the core can be cleared of SO2 before ejection. SO2 is highly
corrosive and pipework must be stainless steel, PTFE or nylon. For large
cores, a separate gassing chamber may be used in which the chamber pressure
is first reduced then SO2 is injected and finally the chamber is purged.
Gas usage: 2 g (ml) liquid SO2 is needed per kg of sand. Cores are normally
gassed for 1–2 seconds followed by 10–15 seconds air purge. Overgassing is
not possible.
Core strength: Tensile strength is 1250 kPa (180 psi) after 6 hours. Storage
properties are good.
Resin bonded sand 197
Casting characteristics: Coatings are not normally necessary and surface quality
of castings is good. Breakdown of cores is excellent with ferrous castings. It
is also good with aluminium castings, better than cold box cores, and this
has proved to be one of the best applications. The sulphur catalyst may
cause some metallurgical problems on the surface of ductile iron castings.
Reclamation: Thermal reclamation is possible. Mechanically reclaimed sand
should not be used for SO2 core making but may be used with furane self-
setting sand.
Environmental: SO2 has an objectionable smell and is an irritant gas. Core
boxes must be sealed and exhaust gases must be collected and scrubbed
with sodium hydroxide solution. Cores must be well purged to avoid gas
release during storage.
MEKP is a strongly oxidising liquid and may ignite on contact with
organic materials. Observe manufacturer’s recommendations carefully. Avoid
skin contact with resin and mixed sand.
SO2 cured epoxy resin
Principle: Modified epoxy/acrylic resins are mixed with an organic peroxide,
the mixture is blown into the core box and hardened by passing sulphur
dioxide gas through the compacted sand. The SO2 reacts with the peroxide
forming SO3 and then H2SO4 which hardens the resin binder.
Sand: Clean silica sand of AFS 50-60. Other sands may be used if the acid
demand value is low. The temperature should be around 25°C, low
temperature slows the hardening reaction.
Resin addition: Typically 1.2–1.4% resin, 25–60% (based on resin) of MEKP
(methyl ethyl ketone peroxide).
Nitrogen content: Zero.
Other details: Similar to SO2/furane process. Bench life is up to 24 hours.
Ester-cured alkaline phenolic system
Foseco product: FENOTEC resin
Principle: The resin is an alkaline phenolic resin (essentially the same as the
self-hardening resins of this type). Sand is mixed with the resin and blown
or manually packed into a corebox. A vaporised ester, methyl formate, is
passed through the sand, hardening the binder.
198 Foseco Ferrous Foundryman’s Handbook
Sand: Highest strengths are achieved with a clean, high silica sand of AFS
50-60. Sand temperature should be between 15 and 30°C.
Resin addition: Typically 1.5% total.
Nitrogen content: Zero, sulphur is also zero.
Mixing procedure: Batch or continuous.
Bench life: Curing only occurs by reaction with the ester-hardener, so the
bench life is long, 2–4 hours.
Core blowing: Blow pressure 350–500 kPa (50–80 psi) is needed.
Core boxes: Wood, plastic or metal. Clean once per shift and use SEPAROL or
a silicone based release agent.
Gassing: Methyl formate is a colourless, highly flammable liquid, boiling at
32°C. It has low odour. A specially designed vaporiser must be used to
generate the methyl formate vapour. Usage of methyl formate is about 20–
30% of the resin weight. Core boxes and gassing heads should be sealed
correctly and the venting of the core box designed to give a slight back
pressure so that the curing vapour is held for long enough for the reaction
to take place.
Core strength: Compression strengths of 5000 kPa (700 psi) are possible.
Tensile and transverse strengths are not available, they are not as high as
phenolic isocyanate resins.
Casting characteristics: Finning and lustrous carbon defects are absent. Good
high temperature erosion resistance and good breakdown. Mostly used for
steel and iron castings.
Environmental: Low odour, but methyl formate is flammable and care is
needed.
Reclamation: Reclamation by attrition is possible but the reclaimed sand is
best re-used as a self-hardening alkaline-phenolic sand where strengths are
not as critical. Core sand residues entering green sand causes no problems.
General: Strengths are relatively low so the process has mainly been used for
rather thick section moulds and cores where high handling strength is not
necessary.
Review of resin coremaking processes
The heat activated resin coremaking processes, Croning/Shell and hot box
Resin bonded sand 199
were developed in the 1950s and 1960s and rapidly supplanted the older oil
sand coremaking process. The attraction was speed of cure and the fact that
cores could be cured in the box, eliminating the dimensional problems of oil
sand cores. By the mid-1970s the amine-urethane cold box process was
becoming firmly established, bringing great benefits of speed as well as an
environmental burden. Since 1976 there have been many further developments
in the amine-urethane systems and in other cold gas hardened core binder
systems.
Reasons for this intense interest include:
The flexibility of gas-hardened processes which makes them suitable for
mass production of cores with automatic equipmentFast curing of cores in the box by controlled injection of reactive gases
High strengths on ejection, often 80% of the final strength
Dimensional accuracy resulting from cold curing
Availability of an extensive range of specially designed core-making
equipment
Energy saving through cold operation
Rapid tooling changes made easy by low tooling temperatures
By 1990 the majority of cores were produced by the cold box, amine isocyanate
process (Table 13.1).
Table 13.1 Coremaking processes used in 48
automobile foundries in Germany, 1991
Amine cold box 44
Hot box 10
Shell/Croning 9
CO2 – silicate 3
Tables 13.2a and b summarise the production features of the many
coremaking processes in use.
Figure 13.5 shows how the use of chemical binders has changed in the
USA over the last 40 years.
Shell sand is declining slightly, holding up remarkably for such an old
process.
Core oil has declined in the face of hot box and cold box.
Silicates received a boost in 1980, due to the introduction of ester-hardening,
but have declined slowly since.
Hot box has declined due to the rise in use of cold box phenolic urethane
core binders, but still has a significant place.
Acid cured furanes have held steady since the maximum in 1980.
Urethane no-bakes are popular in the US, although their use in Europe is
limited.
New binders are predicted to increase substantially by the year 2000.
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1
1
4–
8 
hr
s
1/
2–
1 
m
in
.
0–
2 
hr
s
3
1
1
A
m
in
e-
u
re
th
an
e
1
1
1–
6 
hr
s
10
–3
0 
se
c.
0–
1 
hr
2
2
2
SO
2-
ep
ox
y
1
2
24
 h
rs
10
–3
0 
se
c.
In
st
an
t
1
1
1
SO
2-
fu
ra
ne
2
2
24
 h
rs
10
–3
0 
se
c.
In
st
an
t
2
2
2
C
O
2-
si
lic
at
e
3
1
2–
3 
hr
s
10
–6
0 
se
c.
1 
hr
1
1
1
E
C
O
L
O
T
E
C
2
1
3–
4 
hr
s
 5
–3
0 
se
c.
In
st
an
t
1
1
1
1 
G
oo
d
 –
 u
nl
ik
el
y 
to
 r
es
tr
ic
t 
ap
p
lic
at
io
n
2 
Sa
ti
sf
ac
to
ry
 –
 s
u
it
ab
le
 f
or
 m
os
t 
ap
p
lic
at
io
ns
3 
R
es
tr
ic
ti
on
s 
– 
m
ay
 l
im
it
 a
p
p
lic
at
io
ns
202 Foseco Ferrous Foundryman’s Handbook
Figure 13.5 US foundry industry consumption of sand binder by system. (From
Foundry Management & Technology, Jan. 1995 p. D-5).
U.S. foundry industry consumption of sand binder by system
U
.S
. 
sa
nd
 b
in
de
r 
co
ns
um
pt
io
n,
 I
b 
× 
10
6
300
200
100
0
1960 1970 1980 1990 2000
Year
New binders*
Phenolic urethane cold box
Phenolic urethane no bake
Acid cured furan and phenolic no
bake
Hot box
Silicate CO2 and no bake
Core oil
Shell
*Includes phenolic/ester, warm box,
 polyol urethane, and SO2 cured
 systems.
Exhaust
fans
Exhaust
stacks
Reverse
jet
filters
Fume extraction
systems
Oxidiser
exhaust
stack
Reverse
jet filter
Thermal
oxidiserMachine
enclosures
(11 off)
Amine
collection
system
Figure 13.6 Collection and control of amine gas in a cold box core shop.
The environmental difficulties of the amine-isocyanate process have been
solved, at a cost, by engineering. Figure 13.6 shows how a large coreshop
collects and disposes of amine gas. Smaller foundries find the problems of
handling amine gas difficult so there is a need for a more environmentally
Resin bonded sand 203
friendly process. Up to the present, only the CO2-hardened ECOLOTEC
system meets the requirements.
A growing concern of all users of chemical binders is that of disposing of
used sand. All the developed countries impose severe restrictions on the
materials that can be safely dumped on landfill sites. Pollution of water
supplies by phenol and other leachable chemicals is a growing concern, so
all resin manufacturers are reducing the free phenol content of their products.
The use of sand reclamation, both mechanical and thermal is being increasingly
used by foundries to reduce the quantity of sand that must be disposed to
waste sites.
Chapter 14
Sodium silicate bonded sand
Sodium silicate is a water soluble glass available from suppliers in a wide
range of types specified by the silica (SiO2), soda (Na2O) and water content.
Manufacturer's data sheets specify the ‘weight ratio’ of silica to soda, the
percentage of water and the viscosity. For foundry use, sodium silicates
with ratios between 2 and 3 and water content around 56% are usually
used.
Sodium silicate can be hardened in a number of ways: by adding weak
acids (CO2 gas or organic esters), by adding various powders (di-calcium
silicate, anhydrite etc.) or by removing water. CO2 gas and liquid ester
hardeners are the most widely used of the silicate processes. Silicate binders
have no smell and few health hazards, but the bond strength is not as high
as that of resin binders and, being an inorganic bond, it does not burn out
with heat, so breakdown after casting can be a problem. For this reason,
various organic breakdown additives are often incorporated with the liquid
silicate or added during sand mixing.
Typical data for foundry grade sodium silicate:
Wt Na2O SiO2 H2O s.g. Visc.cP litres/
ratio (%) (%) (%) at 20°C tonne
Low ratio 2.0 15.2 30.4 54.4 1.56 850 641
Medium ratio 2.40 12.7 30.8 56.5 1.50 310 668
High ratio 2.85 11.2 31.9 56.9 1.48 500 677
CO2 silicate process (basic process)
Principle: Sand is mixed with sodium silicate and the mixture blown or
hand-rammed into a core box or around a pattern. Carbon dioxide gas is
passed through the compacted sand to harden the binder.
Sand: Silica sand of AFS 50-60 is usually used, the process is quite tolerant
of impurities and alkaline sand such as olivine can be used. Sand should be
clay free. Low temperature retards hardening, the sand temperature should
be above 15°C.
Binder addition: About 3.0–3.5% silicate addition is usually used. High ratio
Sodium silicate bonded sand 205
silicates give short gassing times, low gas consumption and improved post-
casting breakdown, but high ratio silicate is easily over-gassed, resulting in
reduced core strength and poor core storage properties. Low ratio binders
give better core storage, but gassing times are longer and breakdown is not
as good. Low ratio silicates (2.0–2.2) are usually used.
Mixing: Batch or continuous mixers are used, avoid excessive mixing time
which may heat the sand and causeloss of water.
Bench life: Several hours if drying is prevented by storing in a closed container
or covering with a damp cloth.
Core boxes: Any material; wood, resin or metal may be used but the boxes
must be painted to prevent sticking. Polyurethane or alkyd paints are used
followed by the application of a wax or silicone-wax polish, or STRIPCOTE
AL.
Blowing: High pressure is needed, 650–700 kPa (90–100 psi).
Curing: The correct volume of gas is needed. Undergassing does not achieve
optimum strength. Overgassing leads to reduction of strength on standing.
To ensure correct hardening, a flow controller and timer should be used. If
cores are to be stored for some time before use, it is preferable to undergas.
Higher strength will then be developed on standing. Gassing times are
typically 10–60 seconds, depending on the size of the core.
CO2 gas consumption per kg of sodium silicate (good quality silica sand
AFS 50)
Silicate ratio Time to reach 700 kPa litres kg CO2
(100 psi) compression CO2
strength at 5 l/min
2.0 52 s 300 0.60
2.2 48 275 0.55
2.4 26 150 0.30
2.5 23 130 0.26
Core strength:
as-gassed after 6 h
Tensile 350 kPa 50 psi 1000 kPa 150 psi
Compressive 2100 300 4200 600
Core storage: Overgassing causes cores to become friable during storage
over 24 hours. Careful control of gassing is essential (Fig. 14.1).
206 Foseco Ferrous Foundryman’s Handbook
Casting characteristics: Cores require coating to produce good surface finish
on ferrous castings. Spirit based coatings should be used because water can
soften the silicate bond. No metallurgical problems occur with ferrous or
non-ferrous castings, the binder contains no nitrogen or sulphur. Breakdown
after casting is poor (with ferrous castings) because silicate fuses with sand
above 400°C.
Reclamation: Reclamation is difficult because the binder does not burn out
during casting.
Health hazards: There is very little fume or smell during core manufacture,
storage or casting. Gloves should be worn when handling silicates or mixed
sand.
General comments: The CO2 process was the first of the gas-hardened processes
to be introduced into the foundry and is still one of the easiest and cleanest
processes to use. Foseco and other suppliers have made important
improvements to the process while still retaining its ease of use and excellent
environmental characteristics.
Gassing CO2 cores and moulds
The core boxes are prepared by coating with a suitable parting agent, silicone
waxes can be used but the best results are obtained with STRIPCOTE AL, an
aluminised self-drying liquid.
C
om
pr
es
si
on
 s
tr
en
gt
h 
(k
g/
cm
2 )
40
30
20
10
0 60 120
Gassing time (seconds)
1
2
3
4
(1) Ratio SiO2 : Na2O2.0:1
(2) 2.2:1
(3) 2.4:1
(4) 2.5:1
Figure 14.1 The effect of 24 hour storage of cores gassed for different times as a
function of silicate ratio.
Sodium silicate bonded sand 207
The simplest gassing techniques are based either on a simple tube probe
fitted through a backing plate, or a hood sealed to the open side of the box
with a rubber strip (Fig. 14.2). Gas at a pressure of about 70–140 kPa (10–20
psi) is passed until the sand is felt to have hardened or some white crystals
appear (indicating overgassing). Venting of the boxes and patterns to prevent
dead spots is essential. It is usual to rap the box before gassing to make
stripping easier.
Gas in
Wooden pad
Metal tube
Single probe
Gas in
Pad
Gas in
Wooden pad
Multiple probe
Gas in
Line coupler Hood
Hood
Figure 14.2 CO2-silicate process, methods of gas application.
Control of gassing is improved by incorporating gas heaters (to prevent
freezing of the valves), flow meters and timers so that automatic control of
the volume of gas passed is possible. Not only does this practice economise
on expensive CO2, but the best strength and core-storage life will only be
achieved if the correct amount of gas is used. It is important that overgassing
is avoided, any error should always be towards undergassing. The suppliers
of CO2 gas will advise on the best equipment to use.
Improvements to the CO2 silicate process
Foseco products: CARSIL sodium silicate blended with special
SOLOSIL additions
DEXIL breakdown agent
Principle: The main drawbacks of the basic CO2 process are:
poor breakdown of the bond after casting
poor core storage properties
rather low tensile strength



208 Foseco Ferrous Foundryman’s Handbook
These properties can be greatly improved by special additives, while retaining
the simplicity and user friendliness of the CO2 process.
The CARSIL and SOLOSIL range: These products are a range of sodium
silicate based binders for the CO2 process. They may be simple sodium
silicates which can be used with DEXIL breakdown agent if required, or
they may be ‘one-shot’ products which incorporate a breakdown agent, or
they may (like SOLOSIL) incorporate special additives to improve bond
strength as well as breakdown.
Binders containing high levels of breakdown additives give improved
post-casting breakdown but the maximum as-gassed strength is reduced
and core storage properties are likely to be impaired. The selection of an
optimum binder for a given application is therefore almost always a
compromise. The requirement for high production rates and high as-gassed
strength must be balanced against core storage properties and the need for
good breakdown. The range of binders includes some which are suitable
only for the CO2 process, some which are suitable for self-setting applications
and some which can be used for both processes.
The commonly used breakdown agents are organic materials which burn
out under the effect of the heat of the casting. While solid breakdown agents
such as dextrose monohydrate, wood flour, coal dust and graphite can be
used, powder materials are not easy to add consistently to sand in a continuous
mixer. Liquid breakdown agents are easier to handle, they usually consist of
soluble carbohydrates. The best improve gassing speed without loss of
strength. Some are also resistant to moisture pick-up and their use has
increased the storage life of high-ratio silicate bonded cores.
Sucrose is the only common carbohydrate soluble in sodium silicate without
a chemical reaction. It is readily soluble up to 25% and many sugar or
molasses-based binders are available. Use of sucrose increases gassing speed
but reduces maximum strength and storage properties. Nevertheless silicates
containing sugar are the most popular CO2 binders because of the convenience
of a binder in the form of a single liquid. Molasses can be used as a low cost
alternative to sugar, but it is subject to fermentation on storage. The Foseco
CARSIL range of silicate binders is based on sugar. Some are designed for
use with CO2, others for self-setting (SS) with ester hardeners. Some can be
used for both processes.
The CARSIL range of silicate binders
The extent to which a core will break down after casting varies depending
on the type of metal cast. Low temperature alloys such as aluminium do
not inject enough heat into the sand to burn out the breakdown agent
fully. Indeed, the low temperature heating may even strengthen the core.
In such cases it is useful to add additional breakdown agents such as
DEXIL.
Sodium silicate bonded sand 209
DEXIL 34BNF is a powder additive developed for use with light alloys.
It also acts as a binder extender so reducing the silicate requirement. The
application rate is 0.5–1.5%. It should be added to the sand and pre-dispersed
before adding the silicate.
DEXIL 60 is a pumpable organic liquid which is particularly suitable for
use with continuous mixers.
SOLOSIL
SOLOSIL was developed to improve on the performance of silicates containing
sugar based additives. SOLOSIL is a complex one-shot sodium silicate binder
for the CO2 gassed process. It contains a high level of breakdown agent/co-
binder and offers a combination of high strength and rapid gassing with
good core storage properties and excellent post-castingbreakdown.
The binder is best used with good quality silica sand. Addition levels of
3.0–4.5% are used depending on the application. To take full advantage of
the high reactivity, an automatic gassing system incorporating a vaporiser,
pressure regulator, flow controller and gassing timer is advisable. The high
rate of strength development is shown in Fig. 14.3. While the transverse and
tensile strength developed by SOLOSIL binders are still somewhat lower
than some organic resin binders, SOLOSIL generally proves more cost effective
and overcomes problems of poor hot strength, veining and finning, gas
pinholing and fume on casting which occur with some resin binders.
Self-setting sodium silicate processes
The first self-setting process used powder hardeners. The Nishiyama process
used finely ground ferrosilicon powder which reacts with sodium silicate
generating heat and forming a very strong bond. The reaction also generates
hydrogen which is dangerous. Other powder hardeners (which do not evolve
dangerous gases) include di-calcium silicate, certain cements (such as blast
Product Ratio Additive CO2/SS Comments
CARSIL 100 2.5:1 Sugar CO2/SS Higher ratio for faster gassing,
take care not to overgas. Can be
used with ester hardeners.
CARSIL 513 2.4:1 Sugar CO2/SS Low viscosity binder for easy
mixing in continuous mixers.
Moulds and cores.
CARSIL 520 2.0:1 High sugar CO2 High breakdown, low viscosity.
CARSIL 540 2.2:1 Low sugar CO2 Suitable for moulds or cores.
CARSIL 567 2.2:1 High sugar CO2 High breakdown, good for AI
casting.
Note: Some of the CARSIL binders were formerly known as GASBINDA binders in the UK.
210 Foseco Ferrous Foundryman’s Handbook
furnace cement and sulphate resisting cement) and anhydrite. However, all
powder hardeners are difficult to add uniformly to sand in continuous
mixers, and their reactivity is difficult to control, since particle size and the
age after grinding affect the reactivity of the powder. When liquid hardeners
based on organic esters were introduced, the use of powder hardeners was
largely discontinued.
Ester silicate process
Foseco products: CARSIL sodium silicate binders
CARSET ester hardener
VELOSET special ester for very rapid setting
Principle: Sand is mixed with a suitable grade of sodium silicate, often
incorporating a breakdown agent, together with 10–12% (based on silicate)
of liquid organic ester hardener. The acid ester reacts with and gels the
sodium silicate, hardening the sand. The speed of hardening is controlled
by the type of ester used.
Sand: Dry silica sand of AFS 45-60 is usually used. As with all silicate processes,
the quality and purity of the sand is not critical, alkaline sand such as
olivine can be used. Fines should be at a low level. Sand temperature should
be above 15°C, low temperature slows the hardening.
Additions: Sodium silicates with ratios between 2.2 and 2.8 are suitable, the
higher the ratio, the faster the set. Silicates containing breakdown agents
are usually used, additions between 2.5 and 3.5% are used depending on
the sand grade. The ester hardener is commonly:
Figure 14.3 Strength development of SOLOSIL compared with a conventional
sugar/silicate system
C
om
pr
es
si
on
 s
tr
en
gt
h 
(k
g/
cm
2 )
20
15
10
5
3.5% Solosil
3.5%
Conventional
silicate
40 80 120
Gassing time (seconds)
Sodium silicate bonded sand 211
glycerol diacetate fast cure
ethylene glycol diacetate medium cure
glycerol triacetate slow cure
Proprietory hardeners may be blends of the above with other esters. The
addition level is 10–12% of the silicate.
Pattern equipment: Wood, resin or metal patterns can be used. Core boxes
and patterns should be coated with polyurethane or alkyd paint followed
by application of wax polish. STRIPCOTE parting agent may also be used.
Mixing: Continuous mixers are usually used, if batch mixers are used, the
ester hardener should be mixed with the sand before adding the silicate.
Speed of strip: 20–120 minutes is common with normal ester hardeners.
Attempts to achieve faster setting may result in lower strength moulds
because the work time becomes short. With certain esters there is a tendency
for core and mould distortion due to sagging if stripping occurs too early.
Faster setting can be achieved by using the special VELOSET hardener.
Strength: The final strength achieved is:
Tensile 700 kPa (100 psi)
Compression 2000–5000 kPa (300–700 psi)
Coatings: Spirit based coatings should be used.
Casting characteristics: No metallurgical problems arise with ferrous or non-
ferrous castings. Breakdown is poor unless a silicate incorporating a
breakdown agent is used.
Reclamation: As with all silicate processes, burnout of the bond does not
occur during casting and attrition does not remove all the silicate residue so
that build-up occurs in the reclaimed sand, reducing refractoriness and
leading to loss of control of work time and hardening speed. The VELOSET
system has been specially developed to permit reclamation (see below).
Environment: Silicate and ester have little smell and evolve little fume on
casting. Silicates are caustic so skin and eye protection is needed while
handling mixed sand.
CARSET 500 Hardeners: These are blends of organic esters formulated to
give a wide range of setting speeds when used with sodium silicates,
particularly the CARSIL series of silicates which incorporate a breakdown
agent. For the best results, the silicate addition should be kept as low as
possible in relation to the sand quality and the CARSET hardener maintained
212 Foseco Ferrous Foundryman’s Handbook
at 10% by weight of the silicate level. The speed of set is dependent on the
sand temperature, silicate ratio and grade of CARSET hardener used.
The CARSET 500 series of hardeners
Gel times (minutes) at 20°C
CARSET 500 CARSIL 540 CARSIL 513 CARSIL 100
series 2.2 ratio 2.4 ratio 2.5 ratio
500 8 7 5
511 9 8 6
522 13 12 8
533 19 15 9
544 105 53 21
555 – – 90
Note: The gel time is the time taken for gelling to occur when silicate liquid is mixed with an
appropriate amount of setting agent. The setting times may not be repeated exactly when sand
is present, due to the possibility of impurities, but it does provide a useful guide.
VELOSET hardeners: The VELOSET range is a series of advanced ester
hardeners for the self-setting silicate process. They have been designed to
give very rapid setting speed with a high strength, excellent through-cure
and a high resistance to sagging. Used in the VELOSET Sand Reclamation
Process, they provide the only ester silicate process in which the sand can
be reclaimed by a simple dry attrition process and reused at high levels
equal to those typical of resin bonded sands.
Additions: There are three grades of VELOSET hardener. VELOSET 1, 2 and
3 Binders of ratio 2.2–2.6 are used, lower ratios give inferior strength while
if higher ratios are used the bench life becomes too short. The bench life
obtained is independent of addition level. The level is usually 10–12% based
on the binder. If the sand is to be reclaimed, the addition level of 11% should
not be exceeded.
Bench life (minutes) at 20°C
CARSIL ratio VELOSET grade
1 2 3
2.2 10 7 4
2.4 7 4 2
2.6 4 2 1
When a choice is possible, always use the highest ratio CARSIL binder and
the slowest grade of VELOSET hardener. This provides optimum strength
development.
Sodium silicate bonded sand 213
Mixer: Since VELOSET is rapid setting, it is preferable to use a continuous
mixer.
VELOSET sand reclamation process: With the conventional ester silicate process,
dry attrition reclamation has occasionally been practised but the level of
sand reuse is rarely more than 50%, which hardly justifies the capital
investment involved. With the VELOSET system, up to 90% reuse of sand is
possible using mechanical attrition.
The process stages are:
Crushing the sand to grain size
Drying
Attrition
Classification
Cooling
The reclaimed sand is blended with new sand in the proportion 75 to 25.
During the first 10cycles of reuse, the sand system stabilises and the bench
life of the sand increases by a factor of up to 2. Also, mould strength should
improve, and it is usually possible to reduce the binder addition level by up
to 20% yet still retaining the same strength as achieved using new sand.
Once the process has become established, it may become possible to reuse
up to 85–90% of the sand (Figs 14.4 and 14.5). See also p. 179.
Adhesives and sealants
It is often necessary to joint cores together to form assemblies, or to glue
cores to moulds before closing the mould. A range of CORFIX adhesives is
available:
CORFIX Type Set time Temp (°C) Remarks
grade
4 Stove 30 180–220 High viscosity gap filling
hardening
8 Air hardening slow ambient For CO2 and self-set silicate
21 Air hardening fast ambient Any cold core
25 Hot melt open time 140–180 Core assembly at high rates,
15–120 s shell process
CORSEAL sealants
This is a group of core sealing or mudding compounds for filling out joint
lines, cracks and minor blemishes in cores. CORSEAL is available in two
forms.
214 Foseco Ferrous Foundryman’s Handbook
Figure 14.4 VELOSET reclamation, showing the variation in bench life after repeated
use of reclaimed sand, compared with conventional ester process.
Figure 14.5 VELOSET reclamation, ultimate strength characteristics of reclaimed
sand, compared with conventional ester process.
0 2 4 6 8 10
Re-use cycle
Conventional ester system
VELOSET 1
Sand: 70% reclaimed
30% New Chelford 50
Binder: 3.5% : 2.2 ratio silicate
Hardener: 0.35%
30
20
10
0
B
en
ch
 li
fe
 (
m
in
ut
es
)
VELOSET 1
600
400
200
0
p.s.i. kg/cm2
C
om
pr
es
si
on
 s
tr
en
gt
h
40
30
20
10
Conventional ester system
Sand: 70% reclaimed
30% New Chelford 50
Binder: 3.5% : 2.2 ratio silicate
Hardener: 0.35%
2 4 6 8 10
Re-use cycle
Sodium silicate bonded sand 215
CORSEAL 2 is a powder which is mixed with water to form a thick paste
(4 parts product to 3 parts water). The paste is applied by spatula or trowel
(or fingers) and allowed to dry for about an hour. It may be lightly torched
if required immediately.
CORSEAL 3 and 4 are ready-mixed self-drying putties which are sufficiently
permeable when fully dry to prevent blowing but strong enough to prevent
metal penetration into the joint. Drying time depends on local conditions
and the thickness of the layer applied but should be at least 30 minutes.
TAK sealant
Small variations in the mating faces of moulds due to flexing of patterns or
deformation of moulding boxes and moulding materials may result in gaps
into which liquid metal will penetrate causing runout and flash. This can be
prevented by the application of TAK plastic mould sealant which forms a
metal and gas-tight seal. TAK does not melt at high temperatures and, if
metal touches it, it burns to a compact, fibrous mass. The TAK strip is laid
around the upper surface of the drag mould, about 25 mm from the edge of
the mould cavity and the mould is then closed and clamped. TAK can also
be used to seal small core prints.
TAK 3 is supplied in cartridge form for extrusion from a hand gun, a
variety of nozzle sizes is available.
TAK 500 is ready-extruded material supplied in continuous lengths of
6 mm diameter.
Chapter 15
Lost foam casting
Principle of the process
Unlike any other sand casting process, no binders are used. Pre-forms of the
parts to be cast are moulded in expandable polystyrene or special expandable
copolymers. Complex shapes can be formed by gluing mouldings together.
The pre-forms are assembled into a cluster around a sprue then coated with
a refractory paint. The cluster is invested in dry sand in a simple moulding
box and the sand compacted by vibration. Metal is poured, vaporising the
preform and replacing it to form the casting (Fig. 15.1).
Many problems hindered the development of the lost foam casting process.
By working closely together, designers, foundries, equipment engineers,
polymer manufacturers and coating suppliers have now removed these
barriers, making the process a cost effective way to manufacture quality
castings. The casting of iron components was initially very difficult due to
the formation of lustrous carbon defects on the surface and subsurface
Figure 15.1 The lost foam casting process.
Foam sections Foam assembly Assembled cluster Coated cluster
Fluidize Pouring Compaction Sand fill
TrimQuenchExtraction
Lost foam casting 217
carbonaceous inclusions, which were only revealed on machining. Essential
to the advancement of ferrous lost foam (LF) casting was the development
of copolymers, such as the patented Foseco Low Carbon Bead, which helps
to eliminate these defects and so make the process viable.
Patternmaking
The raw bead to be moulded is purchased from a chemical supplier. It
consists of spherical beads of polystyrene (EPS) or copolymer of carefully
graded size. The bead is impregnated during manufacture with a blowing
agent, pentane. The first step is to pre-expand the bead to the required
density by steam heating. It is then moulded in a press rather like a plastic
injection moulding press. The moulding tool is made of aluminium, hollow-
backed to have a wall thickness of around 8 mm. The pre-expanded bead is
blown into the closed die, which is then steam heated causing the beads to
expand further and fuse together. After fusing, the die is cooled with water
sprays (often with vacuum assistance) so that the pattern is cooled sufficiently
to be ejected without distortion.
The cycle time is dependent on the heating and cooling of the die, a
process which is necessarily rather slow, taking 1–2 minutes for a cycle. The
moulding machines are large with pattern plate dimensions typically 800 ×
600 mm or 1000 × 700 mm so that multiple impression dies can be used to
increase the production rate.
Some lost foam foundries purchase foam patterns from a specialist supplier,
such as Foseco–Morval (in the USA and Canada). Others make their own
patterns. The casting reproduces in astonishing detail the surface appearance
of the foam pattern. A great deal of effort has been put into improving
surface quality and special moulding techniques such as Foseco–Morval’s
‘Ventless Moulding Process’ have been developed to minimise bead-trace.
EPS mouldings for casting have now reached levels of quality and complexity
far beyond that expected from a material designed originally for packaging.
Joining patterns
Where possible, patterns are moulded in one piece using the techniques
developed for plastic injection moulding such as metal ‘pull-backs’ and
collapsible cores, but many of the complex shapes needed to make castings
cannot be moulded in one piece. Sections of patterns are glued together
quickly and precisely using hot melt adhesives using special glue-printing
machines (Fig. 15.2). The adhesive is reproduced in the finished casting so
that it is important to lay down a controlled amount of glue to avoid an
unsightly glue line.
218 Foseco Ferrous Foundryman’s Handbook
Assembling clusters
Some large castings are made singly, the EPS pattern being attached to a
down-sprue of EPS or, in the case of ferrous castings, usually of hollow
ceramic fibre refractory. Smaller castings are made in clusters, the patterns
being assembled around the sprue with the ingates acting also as supports
for the cluster.
Coating the patterns
The foam pattern must be covered with a refractory coating before casting.
If no coating is used, sand erosion occurs which can lead to mould collapse
during casting. The coatings are applied by dipping and must be thoroughly
dried in a low temperature oven before casting.
Investing in sand
The coated pattern clusters are placed in a steel box and dry silica sand
poured around. As the box is filled, it is vibrated to compact the sand and
cause it to flow into the cavities of the pattern. It was the failure to vibrate
correctly that led to so many problems in the early days of lost foam. Followingmuch research by equipment suppliers, good vibration techniques have
been developed and patterns with complex internal form can now be reliably
invested. It is not possible to persuade sand to flow uphill by vibration so
patterns must be oriented in such a way that internal cavities are filled
horizontally or downwards.
The mechanism of casting into foam patterns
When low melting point metals such as aluminium alloys are cast into EPS
Figure 15.2 Sections of patterns are glued together to form complex shapes.
Lost foam casting 219
foam, the advancing metal melts and degrades the polystyrene to lower
molecular weight polymers and monomers. These residues are then
transported through the coating as both liquids and gases into the sand.
This process is illustrated in Fig. 15.3. Failure to remove the gaseous residues
quickly enough results in slow mould filling and misrun castings, Fig.15.4.
If the gases escape too quickly, however, then the metal will fill the cavity in
an uncontrolled turbulent manner giving rise to oxide film defects and even
mould collapse (Fig. 15.5). If the liquid residues are not absorbed by the
coating, a thin carbon film may form on the liquid metal front which, if
trapped, may cause a ‘carbon-fold’ defect (Fig. 15.6).
Figure 15.3 An illustration of the transport of gas and liquid polymer degradation
residues through STYROMOL and SEMCO PERM lost foam coatings.
Figure 15.4 A mis-run defect caused by the use of a coating with insufficient
permeability.
When iron is cast, the higher temperature causes rapid breakdown of the
EPS with much gas formation. Vacuum may be applied to the casting flask
to aid the removal of the gas. High temperature pyrolysis of EPS results in
tar-like carbonaceous products which are not always able to escape from
the mould. They break down further to a form of carbon called ‘lustrous
carbon’ which causes a defect characterised by pitting and wrinkling of the
Metal
Coating
Coating
Polymer
foam
Sand Gas Liquid
Sand Gas Liquid
220 Foseco Ferrous Foundryman’s Handbook
upper surface of the casting. High carbon irons, such as ductile iron, are
most prone to the defect. In the early 1980s it seemed as though the use of
the lost foam process would be seriously restricted by this problem. It was
then found that the polymer PMMA (polymethyl methacrylate) depolymerises
completely under heat to gaseous monomer leaving no residues in the casting.
PMMA is not easy to make in an expandable form and not easy to mould
either. Foseco has developed ‘Low Carbon Bead’, a copolymer of EPS-PMMA
which has moulding properties similar to EPS and eliminates lustrous carbon
in all but the heaviest section castings (Fig. 15.7).
Foseco and SMC have developed STYROMOL and SEMCO PERM lost
foam coatings, designed to remove both the liquid and gaseous residues at
the rate required to give controlled mould filling and defect-free castings
(see p. 239). These coatings include:
Insulating STYROMOL 169 series coatings for aluminium.
Non insulating STYROMOL and SEMCO PERM coatings for grey and
ductile iron.
Figure 15.6 A cold fold defect (on aluminium) caused by poor liquid residue removal.
Figure 15.5 An oxide film defect (on aluminium) caused by turbulent mould filling
through use of a coating with too high permeability.
Lost foam casting 221
High refractoriness STYROMOL and SEMCO PERM coatings for chrome
irons, manganese and carbon steels.
Methoding
Patterns must be orientated to allow complete filling with sand. Ingates
must fulfil the dual role of supporting the fragile pattern cluster and controlling
the metal flow. In aluminium casting, it is mainly the permeability of the
coating that controls the filling of the casting and very gentle, turbulence
free filling is possible with direct pouring. Iron castings, having higher
density and heat content, are usually bottom gated to allow controlled mould
filling.
Advantages of lost foam casting
1. Low capital cost: The capital cost of a lost foam foundry is as little as
50% of a green sand plant of similar capacity.
2. Low tooling cost: Though tools are expensive, their life is long, so for
long-running, high volume parts like aluminium manifolds, cylinder
heads and other automotive parts, tool costs are much lower than for
gravity or low pressure dies which have a shorter life and require multiple
tool sets because of the long cycle time needed for each casting. For shorter
running parts the advantage is less and may even be a disadvantage.
3. Reduced grinding and finishing: There is a major advantage on most
castings since grinding is restricted only to removing ingates.
4. Reduced machining: On many applications, machining is greatly reduced
and in some cases eliminated completely.
Figure 15.7 The use of Foseco Low Carbon Copolymer Bead eliminates lustrous
carbon defects on grey and ductile iron castings.
222 Foseco Ferrous Foundryman’s Handbook
5. Ability to make complex castings: For suitable applications, the ability
to glue patterns together to make complex parts is a major advantage.
6. Reduced environmental problems: Lost foam is fume free in the foundry
and the sand, which contains the EPS residues, is easily reclaimed using
a simple thermal process.
Disadvantages
1. The process is difficult to automate completely; cluster assembly and
coating involves manual labour unless a complete casting plant is
dedicated to one casting type so that specialised mechanical handling
can be developed.
2. Methoding the casting is still largely hit and miss and a good deal of
experimentation is needed before a good casting is achieved.
3. Cast-to-size can be achieved but only after several tool modifications
because the contractions of foam and casting cannot yet be accurately
predicted.
4. Because of 2 and 3, long lead times are inevitable for all new castings.
Applications
The successful foundries have been extremely selective in choosing casting
applications. In general, lost foam is not regarded as a low-cost method of
casting. It is the final cost of the finished component that must be considered.
Aluminium castings
By far the largest proportion of Al castings are used in the automotive
industry so this has proved the biggest market for LF.
Inlet manifolds: This was the first successful application and is still being
used. The usual process for manifolds is gravity diecasting, a slow process
with high tooling cost. Lost foam is used to best advantage in water-jacketted
carburettor manifolds.
Cylinder heads: The fastest growing automotive application. Heads are
conventionally cast by gravity die with a complex package of cores set into
an iron die. Use of LF gives the designer rather more freedom to cool the
working face effectively, the combustion chambers can be formed ‘as-cast’,
avoiding an expensive machining operation and bolt holes can be cast.
Cylinder blocks: Automotive companies are moving away from grey iron
towards Al blocks. LF offers substantial design advantages; features can be
Lost foam casting 223
cast in, such as the water pump cavity, alternator bracket, oil filter mounting
pad. Oil feed and drain line and coolant lines can also be cast more effectively.
A variety of other automotive parts are being made, water pump housings,
brackets, heat exchangers, fuel pumps, brake cylinders. Applications will
increase as designers become aware of the design potential. High strength
parts such as suspension arms have proved difficult because of metallurgical
differences between LF and conventional castings. New developments such
as the Castyral Process in which pressure is applied to the solidifying casting
are being adopted to improve strength.
Grey iron
Modern automated green sand is such a fast and efficient process that LF
cannot compete on cost of the casting alone. Foundries must look for castings
where the precision of LF gives savings in machining costs.
Stator cases: This has proved one of the most successful applications. There
are weight savings of up to 40% to be